self and Self: atman and Paramatman
Do not know the truth: you will get attached to it, and that will be Self-destructive.
The self and Self are two different things as physical entities known to me only as purusho and Purushottama. Mind and atman are non-physical (spiritual) entities reflecting the self and the Self. When you gradually through satya-advaita yoga lose all attachments of the mind the ego vanishes and the mind becomes atman, and the self becomes Self. When one keeps the mind free of attachments it generates awareness (truth of the moment), This is essential for survival with dignity (Purushouttama) To think of the past or the future leads to the destruction of truth in the Self mode of physical operation because reality is transient and impermanent. The atman is Brahman the all-knowing Entity of the Universe (Paramatman) or God Sri Krishna-Durga. This is why it works. This is my version of Vishista-advaita Vedanta.
If you are attached to any thoughts you cannot gain knowledge: the mind needs to be totally free letting awareness to do the necessary probing to realise.
I cannot reason why the mind works like that except to say that when the mind is cluttered with beliefs, thoughts, wishes, desires, anticipations, hopes, expectations, plans, objectives, missions, it is in a state of confusion such that these are stumbling blocks to awareness of the environment, the reality that is transient and impermanent which is what one needs to know in order to be able to determine the reality of the moment, the truth that is necessary for one to live one's life safely and comfortably. When the mind is free of the bodily-brain interactions with it, one is ones true nature, the Self, which is free of all attachments. It is in this Self mode, that one is fully aware of the environment and can take decisions on how to live during one's next moment. One is then fully Self-sufficient and can tackle any hurdles that come's one's way because the awareness of the environment discovers the truth of the situation so one can take the correct actions that threaten a person or which seeks new opportunities. This is the ongoing process of Realisation and it never ends so long as one is alive.