In response to a letter, the Rebbe writes: Concerning the blessing you received from my father-in-law, you have the choice whether to worry if the blessing will or won't materialize - and when it finally does materialize you will be doubly burdened as to why you wasted so much energy worrying in vain - or you may choose to be strong in your faith and trust that G-d will lead you on the straight path and fulfill all your needs. Then you will be able to say: look how well I handled the situation, that I didn't worry about things there was no reason to worry about.

Igros Kodesh of the Rebbe, vol. 4, p. 256