Why is making a small change so difficult?

Next time you pull out your hair because your spouse, friend, or coworker (or you) can’t seem to change his or her habits, think about this (from Scott Young):

One of the biggest mistakes I’ve made when trying to change habits, is simply in underestimating the amount of conscious focus keeping the habit will take. In many ways, making big changes for diet, exercise or sleep is easier than making a little change because it is too easy to undervalue exactly how much emphasis is required to make the change.