You Never Know

Even if someone has davened for the same thing for many years and it seems that he has not accomplished anything, he should not stop davening for it. In the end he will see that his tefillah helped him tremendously. The Midrash Shmuel (ch. 4) teaches that some tefillos help immediately, some after three days, and some after thirty years! The important thing is to realize that when it seems that one’s tefillah has had no effect, this is not true. It could be that if he had not been davening all along, the situation would be much worse than it is, and his tefillah had a partial effect, as Rabi Yehoshua ben Levi said (in Vayikra Rabbah).

(Chayei Olam by the Steipler Rav zy”a, ch. 28)