I once saw Rabbi Yisroel Baal Shem Tov in a dream, and I asked him a question. When I began to serve Hashem, visiting tzaddikim, and learning from the them, I made avodas Hashem my business. At that time, I felt an improvement each day in my study, kavannah in my davening, and other deeds. But now I feel no improvement whatsoever, and one day seems like the next.
He replied by giving me an example. When a child first begins to learn the alef beis, his daily improvement is very obvious. One week he only knows one lesson, and the next week he knows two. But when he grows up and becomes more advanced in his studies, there is no obvious daily improvement, even though he is able to do importance research. Still, if one considers it, he accomplishes more each day than the small child can in a year.
(Maggid of Koznitz)