If you are having difficulty getting out the door for a run, try this:
I'll use running as an example...but it can be any workout...or any discipline for that matter. Put on your best gear. Tell yourself you will exercise for 3 minutes; i.e. walk a minute, jog a minute, walk a minute. If this is too psychologically daunting, set an even more manageable goal; i.e. walk 1 minute. Keep reducing your goal until you arrive at one that you feel you can do. It doesn't matter what you pick as your goal. The only thing that matters is that you know you can do it. It should not be daunting in any way.
Then...don’t judge it. Just go do it. Ignore the critical voices in your head that will inevitably yammer away. Recognize them for what they are...the ego doing its bit. Pay attention to what you are doing. If you feel like continuing, go ahead. See what happens.
The most important thing is to get out the door and take a step. Begin. Once you've started, it's a success. The Resistance is greatest when you are trying to begin.
The persistence you develop through running will carry over to all aspects of your life. It's worth developing.
I got the following saying from Dan Millman, author of "Way of the Peaceful Warrior:
"A little bit of something is better than a lot of nothing."
I find myself saying it all the time. I pretend I came up with it...hee hee...