Let's say I say, "Today I'm going to make this day the best day of my life." For a day, maybe two, I can actually make it work.
After that, I can't do it anymore. That "magic" idea that it's something new and beginning again is lost, and I'm even more disheartened than had I not tried to do something.
There's that overused aphorism that every journey begins with a single step. The problem isn't the first step. It's all the steps that come after it.
So after a while, you stop walking, stop talking, stop everything. I can't even get mad any more. I'm more than tired. I'm spent.