The Talmud here is simply informing us of a reality that these four activities will naturally weaken if we don't strengthen them in the same way that our muscles weaken if we don't excercise them. How much excercise does a person need? If he's in bad shape he needs a lot. If he's in good shape he needs a program of maintenance which takes less time. The same is true here: if he's strong in one of these areas he just needs a maintenance program. If he's week in a particular area he needs more of a development program. And, of course, in deciding which one to do devote time and energy to he should choose the area that he is weakest in.

Kol Tuv,

Yonasan Sigler

This is not a Psak Halachah