Attaining Siddhi in Yoga

You must gather yourself within more firmly. If you disperse yourself constantly, go out of the inner circle, you will constantly move about in the pettinesses of the ordinary outer nature and under the influences to which it is open. Learn to live within, to act always from within, from constant inner communion with the Mother. It may be difficult at first to do it always and completely, but it can be done if one sticks to it —and it is at that price, by learning to do that that one can have the siddhi in the Yoga.

Ref: Letters on Yoga Vol. III