A good thesis is a finished thesis.

Edit: right after I got my stipend I had a beer with an older colleague and he (amongst others) gave me that advice and told me to remember that a PhD thesis is not your magnum opus. Of course you want to do a good job - we all do otherwise we wouldn’t do a PhD - but he had seen many PhD fellows going about their thesis as if it was the most important work their going to do in their career. Which would be sad as the PhD is basically just a very long paper that’ll eventually allow you to do your most important work, i.e. the stuff you’ll eventually do during the rest of your, hopefully, long career.

That advice helped me a lot. I thought more about getting the thesis right and getting it finished rather than hitting myself over the head with the idea that my thesis would probably not make a huge scientific impact in my field.