Inner Guard

It is mainly an inner guard that you must keep. At the same time, if you feel unease in crowds it is better to avoid them—except in case of music if you feel secure there. A crowd of people engaged in purely social interchange is necessarily on a lower level of consciousness in which undesirable forces may move, if there is anyone there open to them, and one who is in a stage of consciousness opening to higher things but not yet fixed in steady and self-supporting calm is safer away from it.

In sadhana one is supposed to keep outward forces at a distance or at least not to allow them to invade one. If one faces a difficulty in the right spirit and overcomes it, naturally one progresses, but that is a different thing from letting alien forces or influences enter into the conscious being. No one need invite that,—they are only too ready to do it without being invited. One can look at and become conscious of all forces, even the worst, darkest and most hostile, provided one remains on guard and refuses all credence or support to their suggestions and rejects all claim of theirs to a place in the consciousness and nature. But all cannot do that in the earlier stages.

Ref : Letters on Yoga Vol. II