DEUT1566 [Judah b. Tema] used to say: … the man of forty [has attained] understanding; Pirkei Avot, Perek V, mishnah 24. Just as thirty finds a man at the peak of his strength, so forty finds him at the height of his powers of understanding. At the end of the Israelite wanderings, when those who left Egypt had died out, Moses told the next generation, born after the exodus, "I have led you forty years in the wilderness…" and just before this, Moses told them, "the Lord has not given you a heart to know, and eyes to see, and ears to hear, until this day." It took them forty years to realize the full significance of their extraordinary experience. "From this you can learn," said Rabbah, "that a man does not fully plumb the thinking of his master teacher until he is forty" (Deuteronomy 29:4,3. T.B. Abodah Zarah 5b (in place of Rabbah, M'iri and En Ya'akov have Rava). For at this age, R. Bahya observes, the physical state is definitely on the decline; and as physical ability wanes, mental powers grow stronger and clearer. The focus can be sharper, the vision brighter, to grasp wider. Experience adds perspective and depth to mature understanding.