The inevitable descent of the Supramental

If the supramental descent is decreed, nothing can prevent it; but all things are worked out here through a play of forces, and an unfavourable atmosphere or conditions can delay even when they cannot prevent. Even when the thing is destined, it does not present itself as a certitude in the consciousness here (Overmind-mind-vital-physical) till the play of forces has been worked out up to a certain point at which the descent not only is, but appears as inevitable.

Ref: Letters on Yoga Vol. I