‘Seeing’ a snake in a rope is one thing, and ‘the ego’ is another thing, though both are ‘mistakes’, mistaken perceptions. The 1st is a mis-perception through the sense of vision producing a (temporary) wrong belief, whereas the 2nd (the ego) is a wrong or mistaken or unsupported belief. Thus, the mistake abut the ego is that, though it is a generally widespread belief (in separate, individual, existence), it is only a belief, a psychological construct not existing in reality. It is in the same category – ‘non-existents’ – as ‘the son of a barren woman’ or ‘a hare with horns’. The subject is subtle, with no straightforward differentiation between one category an another of the three listed here (underlined); for example, a mirage, and everything given in sense experience but not having an objective counterpart, belongs to the category of ‘illusory things’. The problem with the ‘ego’ is that ‘it’ has a basis in reality: the subjectivity of Consciousness, there being no other subject or subjects, and hence the sensation or feeling of being such (a subject) in the ‘individual’ human being, leading to the mistaken belief in his/her autonomy as an agent (doer, enjoyer, etc.). That is why we call it a mistake, a non-entity, non-existent. This needs careful investigation, since there is a great deal of confusion and different viewpoints about this impostor (not a ‘real’ impostor, usurper, but a wrong belief). Generaly, most readers, at least initially, will not accept this advaitic (non-dual) doctrine, as just briefly expounded.
‘The world is illusion’ only from a higher vision – and also from modern science – but from the empirical, conventional perspective, tables and chairs, people, minds, ‘good and bad’, life and death, etc. are “real existents”.
‘The world is real’, from the highest perspective – Atma-Brahman (or Consciousness) being the only reality, ‘One without a second’; everything else has its reality in ‘God’, reality per se, or Consciousness. (There is no death, as there is no birth; no ignorance, no multiplicity, no suffering or imperfection). All this is held by the sages.