Just by performing all kinds of yoga practice, breathing exercises, relaxation, cleansing exercises, chanting, concentration and meditation practice regularly for years and years, and experiencing or attaining certain momentary side-effects from the practice, or one has been actively performing many kinds of ritual or charity work, and the mind might feel good, calm and meaningful, but if without working on eradicating ignorance and egoism, it doesn't lead towards self-realization and liberation.
The teachings of yoga and buddhism are not different from one another, even if there are some influences of Hinduism in yoga. Some people might misunderstood that buddhism and yoga is a form of religion belief and practice. They are not a religious belief or practice. The truth of names and forms, of selflessness and impermanence, is not a belief. It's what all kinds of names and forms are. It's science. There's no superiority or inferiority, authority, authoritarianism, miracles, believer, follower, judgment, punishment, or sin. There's only cause and effect, actions and consequences of actions, selfless impermanent changes, suffering, the cause of suffering, the path of self-realization, the selfless practitioner, direct experience and realization, ignorance or void of ignorance.
One doesn't need to have a religion, or believe in 'the creator of the universe' or 'the soul/spirit', to be practicing yoga and/or buddhism, and realize selflessness. One also doesn't need to be physically healthy, fit, strong and flexible, or mentally intelligent and knowledgeable, or perform any ritual, or know any chanting and prayer, to realize selflessness. Regardless of whether one hasn't done any good deeds or one has done many bad deeds, one can still practice yoga and/or buddhism and realize selflessness, under correct understanding and right effort. It's unlimited by any quality of names and forms.
The approach might be different, but the direction and the goal is the same. Both are leading towards non-separateness, or non-discrimination towards all kinds of names and forms being what they are, under the presence of right discrimination or correct understanding.
Self-inquiry towards what is 'I', and inquiring towards the truth of everything, including all the teachings of yoga and/or buddhism is highly important for those who want to attain self-realization towards selflessness, under the intense yearning for liberation. There's neither right nor wrong with certain minds are interested in yoga or buddhism under the ignorant selfish desire of attaining super extra ordinary mind power to be gratifying all desires, to be controlling others to be and not to be in certain way, or to be defying selfless impermanent changes, but that won't lead the mind towards the liberation from ignorance and suffering, or the attainment of self-realization, as the mind doesn't work on eradicating ignorance and egoism.
Not by coming in contact with and knowing the teachings through hearing from someone or reading many books written by someone about yoga or buddhism, but coming from this mind itself to inquire towards the truth of everything. The teachings or the dhamma has no super extra ordinary power, even when one memorizes all the teachings word by word, but it's the direct realization towards the teachings or dhamma, that will liberate the mind from ignorance and suffering.
Siddhartha Gautama never wanted to have all his teachings to be written down in text form, and he insisted that all and everyone must perform inquiry towards the truth of everything, including all his teachings, to be attaining direct realization towards the truth of everything, without blind-believing, blind-following, blind-practicing, blind-agreeing/disagreeing, or blind-propagating.
Even though the truth of everything, or the teachings, or the dhamma, can never be contaminated, or destroyed, or changed, never increased nor decreased, however, the limited reasoning, interpretation and understanding of the minds under the influence of ignorance and egoism can be faulty or corrupted, and hence, misinterpreting and manipulating the truth of everything/the teachings/the dhamma into something else, particularly to be the way that they prefer, like and desire, while the truth of everything/the teachings/the dhamma, is still what they are, not being affected, determined or contaminated by such misinterpretation and manipulation deriving from the wild imaginary passionate egoistic minds functioning under the veil of ignorance, and being conditioned by certain worldly passionate egoistic thinking, belief, values and practice.
Inquire towards these essential teachings -
There's only NOW. Existence, and the mind awareness/perception/cognition towards the selfless impermanent existence, is only in NOW. There's neither past nor future. In NOW, there are selfless impermanent changes. In NOW, some are arising, changing and decaying, some are passing away, some had passed away. In NOW, someone or something is a few hundred or thousand kilometer from here. In NOW, the same someone or something is right here. It is the ceaseless selfless impermanent changes and/or motions in NOW that generates the false impression or perception of TIME, of speed, distance, day/night, week, month, year, past, present and future. In stillness, void of motions, and if without selfless impermanent changes of names and forms happening in the silent infinite limitless space, what is time, or speed and distance, or day and night, or past and future? There's only NOW.
If Swami Sivananda is still living, that selfless physical body would be very old in NOW. If Siddhartha Gautama Buddha is still living, that selfless physical body would be extremely very old in NOW. However, their physical body ceased existing, or are not existing, in NOW. That's all.
Regardless of living sentient beings or non-living objects, all are selfless and impermanent.
The realization towards TIMElessness, or the correct understanding towards TIME, doesn't change or stop the selfless impermanent changes continuously happening in the selfless impermanent existence of all kinds of names and forms in the space of the universe, including the selfless impermanent existence and function of the selfless physical body and the selfless thinking faculty that is here perceiving all these, selflessly. It's solid concrete science. Nothing mystical or magical about the direct realization or correct understanding towards the truth of names and forms, void of ignorance towards the truth of everything.
Upon the direct self-realization towards selflessness, upon the annihilation of ignorance and egoism, upon the annihilation of the restless selfless modifications of the selfless mind (In stillness and silence, void of motions or activities), upon the realization towards TIMElessness, there's neither births nor deaths. Ceaseless births and deaths (ceaseless impermanent changes/ceaseless thought activities arising and passing away) only exist in the names and forms under going selfless impermanent changes and motions.
What is reincarnation in different realms?
What is the world of selfless impermanent names and forms?
What is the worldly selfless life existence of a selfless physical body and selfless thinking mind?
Who is father, mother, brother, sister, wife, husband, son, daughter?
What is the physical body?
What is the thinking mind/the thinking faculty?
What is the restless modification of mind?
What is restlessness?
What are the states of mind?
Why are the different states of mind?
What is suffering?
Who is suffering?
What is the end of suffering?
What is cause and effect?
What is past, present, future karma?
What is selfless impermanent changes?
Who is going through selfless impermanent changes?
What is restless births and deaths in different realms?
Who is going through restless births and deaths?
Who is going through ceaseless reincarnation or births and deaths in different realms?
What is consciousness?
What is awareness?
What is ignorance?
What is egoism?
What is the ego?
What is 'I'?
What is selflessness?
What is intentionlessness?
What is impermanence?
What is time?
What is timelessness?
What is limitation and condition?
What is limitless and unconditional?
What is mind purification?
What is silence?
What is liberation?
Who is liberated?
What is fear?
What is fearlessness?
Why did Siddhartha Gautama Buddha not mentioning or commenting towards 'the creator of the universe' or 'the soul/spirit'?
Why did Swami Sivananda mentioning the same essential teachings or messages repeatedly, over and over again, either during giving dhamma talk, or as written in all his books?
Why both yoga and buddhism emphasized on the annihilation of ignorance and egoism, mind purification, simplicity, contentment (non-greed), non-possessiveness (non-coveting), non-violence (void of anger and hatred), right understanding, right discrimination, right effort, right view, right livelihood, truthfulness, dispassion, desirelessness (non-craving and non-aversion), non-attachment (non-clinging), detachment (letting go), renunciation, seclusion, solitude, self-control, self-discipline, self-effort, self-independence (mental and emotional independence), self-inquiry, self-realization, direct experience, meditation, stillness, silence, non-dualism, oneness, non-separateness, selflessness, intentionlessness, attributelessness, namelessness, formlessness, selfless impermanent changes, unconditional peace, wisdom and compassion?