You should be able to say "I am", but not "I exist", the two being quite different in that the former only points towards 'inner' and ever present certainty, while the latter asserts objective reality. The inner certainty is not to be found, since it can never be lost; anything that can be lost is not it. Hence you should be more friendly towards teachings which deny any special status to the subject, which hold out no position for the observer who is outside of the system; it is not that you would deny the subject, but that any notion of the subject is already within that system, within some version of the objective totality, the 'mnemonic mass' of ordinary reality. There appears to be a series of realisations, small nudges which move you a step. The journey proceeds by these increments, but there is no map and you don't create such a map or path by following it. It is only when it is impossible to say how you got here, that you find you have arrived.