What's your relationship with your To Do list? Do you look at it with admiration and confidence that it will serve its purpose of helping you accomplish all the things you need to get done each day? Or do you look at it with fear and maybe a little loathing, always hearing a voice in the back of you mind that says, "Yeah - right. Good luck with that!" If you're in the latter camp, perhaps you'll benefit from a little shift in perspective.
Try this. The next time you write a to-do list, don't write a "to-do list." Write a "tracking list." This takes off a lot of the pressure to do it all. If you're in a really bad place, it takes away that story that goes something like, "I'll never get all this done. Why even try??!"
If I, personally, were to write a to-do list that included all the things I'd like to accomplish in the next weeks, months and years, it would be hundreds of items long. And here's the thing - those hundreds of things will change, even in the next few days, due to both internal and external forces. And that would make me crazy because how am I supposed to do THAT MANY THINGS, especially if they're always changing??
On the other hand, a Tracking List is a way of noting what opportunities and obligations are flowing through your life right now without saying you have to do them all RIGHT NOW. Instead, you can note, them and then, over time, review and revise them and work on a select few of them when it's right for you. Sometimes you'll change your mind ("Getting a dog right now seems like too much work") and sometimes outside forces will change your mind for you ("Now that my dad is sick, I can't postpone that trip home any longer.") When you're looking at a tracking list (especially if you do it with your calendar alongside you), it's a lot easier to decide what's actually, really important. Then you can make a short to-do list for today, and be satisfied that you've done your best.