J is for Just Do It.
It might be best known as an advertising slogan for Nike, but there's a lot of truth in the phrase "Just do it".
There are almost as many reasons for not doing things as there are things to be done. Maybe the task will be too difficult. Maybe you're scared that you'll say the wrong thing. Maybe you don't enjoy the task. You might be afraid of looking foolish, or that you won't know anybody or find anyone to talk to you. It could be that you know full well that you can run those two miles, but you don't relish the effort involved in your daily jog.
If you can't think your way out of this paralysis (and more often we think our way into this state, not out of it!) then the best course of action is just to do it.
Like throwing yourself into that not-quite-warm-enough swimming pool, it might be a bit of a shock initially but you'll soon get used to the situation and might even enjoy it. Whatever the fears or worries that were holding you back, they're almost always worse in your head than in reality. The exercise feels good once your feet hit the pavement; mopping the kitchen floor isn't fun, but isn't as bad as you were making out; the phonecall hasn't followed any of the hundred possibilities you played out in your mind, but the person you're talking to hasn't hung up in disgust...
And once you've done whatever it was that you didn't want to do, make a mental (or a written one if you like) to remind yourself that it wasn't as bad as your imagination was making out beforehand. The world didn't end, you're still living... and you've accomplished something too. Then next time it'll be a teensy bit easier to say to yourself "Just do it."