What is outside their grasp, however, is the behavior of other people. It's this that seems to make them more despondent than anything else.
You may have tried your hardest to change your partner for the better -- say, to be more helpful around the house -- to no avail. You might be pushing your friend to hang out with you more often, but she seems to have time for everything and everyone except you.
We've all been there.
As long as you've done your part and expressed how you feel, there's no reason to feel dispirited over that which you cannot change.
We can't will others' behavior to be how we like. People will always do things that will upset us. Unfortunately, as much as we may plead for people to be more considerate of our wishes, some are like impregnable walls -- completely stuck in their ways.
The sooner you accept people for who they are and move on with your life, the happier you'll be. Never let your happiness be contingent upon others. That would be giving them too much power over your own life, and it's just not worth it.
Accept and quit beating yourself over things that are outside of your control.