My observation is it's an equation between:

1) reward/incentive/expected good feelings

2) effort/displeasure of doing the thing and the result

One way to increase #1 is to make it more socially involved. If you're working on a project solitarily, start going to events and talking about it with people, or write about it online. Humans are massively socially motivated.

For #2, one way to address this is with emotional processing. Often something is unpleasant because it reminds of something we didn't like from the past. So really digesting those emotions can allow the expected displeasure to fade because we kind of integrate it into our brains/bodies. But the key for this is that it has to be emotional processing, not intellectual processing.