In letter 1,15a the Steipler wrote, "Experience shows that the more a person overcomes his nature it becomes easier and easier for him to continue to do so until eventually the test will be negligible."[We see this in the Talmud Sanhedrin 107A"There is a small limb, if a person starves it, it will be satisfied; but if he feeds it, it will be hungry."]
In letter 1,15b he adds, "We have to realize that every time one passes this ordeal it becomes easier the next time because this is the nature of this test, if you starve it, it is satisfied, like the Sages tell us in Sanhedrin 107. It is a tried and tested fact that in the end there will hardly be any challenge at all. One has to know that if he sins one time on purpose, it is not only a sin for that moment but the terrible effects continue for a long time, God should protect us, because one deed leads to another, like we learnt in Avos."