Sri Aurobindo
Letters of Sri Aurobindo
Volume III - Part 1
The up and down movement which you speak of is common to all ways of Yoga. It is there in the path of bhakti, but there are equally alternations of states of light and states of darkness, sometimes sheer and prolonged darkness, when one follows the path of knowledge. Those who have occult experiences come to periods when all experiences cease and even seem finished for ever. Even when there have been many and permanent realisations, these seem to go behind the veil and leave nothing in front except a dull blank, filled, if at all, only with recurrent attacks and difficulties. These alternations are the result of the nature of human consciousness and are not a proof of unfitness or of predestined failure. One has to be prepared for them and pass through. They are the “day and night” of the Vedic mystics.
As for surrender, everyone has his own first way of approach towards it; but if it is due to fear, “form” or sense of duty, then certainly that is not surrender at all; these things have nothing to do with surrender. Also, complete and total surrender is not so easy as some seem to imagine. There are always many and large reservations; even if one is not conscious of them, they are there. Complete surrender can best come by a complete love and bhakti. Bhakti on the other hand can begin without surrender, but it naturally leads, as it forms itself, to surrender.
You are surely mistaken in thinking that the difficulty of giving up intellectual convictions is a special stumbling-block in you more than in others. The attachment to one’s own ideas and convictions, the insistence on them is a common characteristic and here it seems to manifest itself with an especial vehemence. It can be removed by a light of knowledge from above which 
gives one the direct touch of Truth or the luminous experience of it and takes away all value from mere intellectual opinion, ideas or conviction and removes the necessity for it, or by a right consciousness which brings with it right ideas, right feeling, right action and right everything else. Or else it must come by a spiritual and mental humility which is rare in human nature – especially the mental, for the mind is always apt to think its own ideas, true or false, are the right ideas. Eventually it is the psychic growth that makes this surrender too possible and that again comes most easily by bhakti. In any case, the existence of this difficulty is not in itself a good cause for forecasting failure in Yoga.