Mori V'Rabi HaRav Schachter gave a speech at YU last week and in it said that there is a Gemarah that says that people who are learning Torah and are keeping Mitzvos also need Chizzuk. Where is this Gemarah?
The Rabbis taught in a braisa: Four things need Chizzuk, as follows: Torah, good deeds, prayer, and worldly affairs.
From where do we know Torah and good deeds? As it says, "Just be strong (chazzak) and valiant (v'ammatz) to observe and perform according to the whole Torah (Yehoshua 1:7)." "Be strong" in Torah, "and valiant" in good deeds.