Michtav M’Eliyahu(1:113):Point of free‑will- When two peoples are fighting each other their war is at their point of contact. Whatever is behind the army of one side – it is totally under their control and there is no opponent at all. Similarly whatever is behind the second army is entirely under the control of the second nation. If one side defeats the other side and pushes them farther back – then the renewed battle takes place where the armies now meet each other. However at the former point of confrontation – there is no longer battle taking place because it is now under one sides control. Therefore in reality there is only one front but potentially the entire area of the two countries can be the place of battle. The same thing can be said about free‑will. Everyone has free‑will – which is the point of meeting of his truth with the imagined truth – the outcome of falsehood. However most of his deeds are not at a place where truth and falsehood meet each other at all. For example there is much truth that man is educated to do and it would never occur to him to do the opposite. Similarly there are is much evil and lies which he is not aware that it is not fitting to do. Free‑will is only applicable at the point of contact between the armies of the yetzer hatov and the yetzer harah. Many people are constantly transgressing the laws of lashon harah because of habit and it never occurs to them that this is bad behavior. At the same time these people have no temptation to transgress Shabbos or not to pray or to ignore tzitzis or tefilin and other such things. That is because they have been educated and habituated in Shabbos, tefilin, tzitzis and other such things to such a degree that the yetzer harah has no chance of influencing them. However this point of free‑will does not stand constantly at one place. That is because if a person choses good a person goes up in level. Therefore by chosing good – those places that were previously under the influence of the yetzer harah – now come under the domain of the yetzer hatov. Those good deeds will now be done without any war or free‑will choice at all. This is what is meant by “mitzva causing mitzva”. Similarly the reverse is true. If he chooses bad, it pushes the yetzer hatov away from its place. Then when he continues to do bad, it will be done without free‑will choice because the yetzer tov had no presence in that place. This is what is meant in Avos (4:2) that “sin causes sin” and also “If a person does a sin and repeats it it because like it was permitted” (Yoma 86b).