Suffering increases your inner strength. Also, the wishing for suffering makes the suffering disappear. Dalai Lama
We say that we have trouble in concentrating because of too much distraction. But it can be said that suffering is also a form of concentration and to be a spontaneous mind process in sense that we have nothing but pains itself in case experiencing extreme pains. From this point of view, it is possible to understand why ascetics chose suffering as a tool for meditation. Because it is the nature of everyone to be reluctant to suffer from pain, it is not an easy option to choose pains for achieving concentration without distraction. It's irony that pain itself is just kind of mind. Body itself doesn't feel pains.