Leave yeshiva if lack the abilty to understand Torah

Igros Moshe (YD IV #36.13) Question:What should a yeshiva student do if he isn’t successful because  he isn’t smart but he is successful studying other things. Answer The fact is that concerning Torah study it is possible that all who study to grow in Torah. Even those who lack the ability for depth they still remember things and that is sufficient to know the entire Talmud as well as the commentaries and halacha at least superficially and that is a major accomplishment. It is possible that if he learns a lot he will also develop the ability to go in depth and get greater understanding both by natural processes and heavenly assistance and eventually become great in Torah knowledge. In contrast if he misses proper understanding of medicine it could result in someone being harmed . This is a common problem with  doctors and other professions. While studying Torah he can rely on his faith and trust in G-d to be successful which isn’t so for other endeavors. In fact if he leaves yeshiva his faith and bitachon generally diminishes.