Not a book, but an article

What worked for me was the realisation from articles like that, that I wasn't lazy or unmotivated, just in a loop of: some reluctance to get started → distraction → feeling bad about not having started yet → distraction → feeling even worse → distraction → ...

It was pretty much an emotional management issue rather than a motivation of focus issue.

The solution wasn't to try harder, be more disciplined or structured or anything. The solution for me was to learn to identify the feeling and take a moment to go "I am feeling reluctant to start this and want to do something else. I'm feeling bad which is ok. Now I'll just get started anyway until the feeling goes away" and usually once I got going I felt a bit better

Pretty much I dissociate for a little bit, which sounds bad but it really works for me. The bad feeling for me is mostly at the start, and once I'm actually making progress, that feels good

Longer term I have learnt ways to make getting started easier

• For a cognitively heavy task I try to make the first step easier; e.g. before I leave it one day, I make a note of what the next thing to do is, which means starting it takes less effort.
• For a manual task that is hard to keep doing because it's mentally unstimulating, I do it while listening to an audio book or while having a phone conversation.
• For any big task I try to find small bites I can do and feel I have made progress, so I get a mental reward rather than an insurmountable thing. Even if the big thing is 1000 small bites, if I just make regular progress I will get there in the end.

The more I do these things, the less bad feelings I have about these tasks

Everyone is different and your tools might end up looking different, but there are probably ways you can get past it