Yes I agree if your 'immovable thing', for example the problem that would need a risky fix that nobody fully understands, can remain without much impact for the

Yes I agree if your 'immovable thing', for example the problem that would need a risky fix that nobody fully understands, can remain without much impact for the rest of the application's life. Sometimes I find I can move towards fixing something difficult in multiple steps as I apply successive features etc. I find that even just documenting the problem in the affected parts of the code can be a good first step. If something changes once it often changes again and I'll move it forward a bit more next time. My theory is that the movement is the important thing, not the arrival at some particular point.