Unpleasant and Overwhelming

Alan Lakein in How to get control of your life and your time lays down
the two basic reasons why we avoid doing things, even avoid thinking them:
because they're unpleasant, or because they're overwhelming. He has a
chapter about dealing with each of those.

For unpleasant, as I recall there are some visualization things, imagining
yourself doing it and it going well or else imagining some ridiculous
catastrophe, and (presumably as a last resort) telling yourself what bad
thing will happen if you don't get it done. For overwhelming it's largely
a matter of figuring out how to break it down into less overwhelming
chunks. One tactic is what he calls the swiss cheese method: make a big
list of tasks that can be done in 5 minutes that will result in progress
on that project, however tiny. Then start knocking them off. Not only can
you cut down the size of a project in that way, by punching a lot of
holes, but also sometimes doing a tiny job leads you to continue working
steadily.

I think the most powerful insight here is just that there are these two
different reasons why you procrastinate on things, and that they take two
different sets of approaches to deal with.