A prerequisite to the inner peace of the soul is to maintain position stillness. We need to learn to sit in one place. You may have marked that you have no control over your body, hence cannot sit or stand or sleep in the same position for an extended period.
If you can’t control your body, how can you possibly control the mind? If one cannot control their mind, how can one control his emotions? One who cannot control his emotions is perennially in a state of restlessness.
The aim of Thanenam is to gain control over emotions.
Our decisions are also wrong when we cannot control our emotions since negative emotions drive them. Positive emotions are needed to make the right decisions and to experience positive emotions; we need to maintain calmness of the mind, for which we need to control our position stillness (Thanenam)
We cannot master Thanenam because we cannot sit still in one place due to the countless memories of Chanchalta (waveringness/restlessness) accumulated in past lifetimes.
You need to resolve once, to overcome this problem and you shall be able to control your body successfully. Once you do this, your mind will automatically come in control, and once that happens, your life, nature, social behavior, emotions, actions, thoughts will all come in control. You shall experience an internal peace within.
Position stillness is a means to establish (Sahkarmita), same karmas as your Guru and your Parmatma (supreme soul). If my Guru, my Parmatma, are calm and blissful, I can achieve the same; I want to be calm and still like them. Hence I need to do the Sadhana of Thanenam.