Will gets built in boring repetitions, the same as anything physical. Not by resolving to become a more patient person, but by ten minutes of not reaching for the phone. By finishing the dull task at the end of the afternoon. By letting a queue be a queue.
Each repetition is trivial and mildly unpleasant and achieves almost nothing on its own. What accumulates is not exactly a virtue. It is a slightly longer fuse, and a slightly longer fuse is enormously useful on the days that need one.