We often get the advice to power through, not give up and various other words to the same effect. We often think these things to ourselves as well, of course and this is very true of our miniatures. This one is relevant to both painting and sculpting.
During our work we often discover that we've done something wrong or something stupid and we try to fix it. There's that bloody minded way that we will work through the problem and somehow compensate or fix it further down the line. These mistakes can be many and varied in their content but a lot of them transpire very early in the process. Maybe your armature wasn't quite right or you picked initial colours on your figure that will make it difficult to get the result you want. You can usually minimise the mistake's impact in one way or another but it tends to be a lot of annoying work and we will often spend a huge amount of time on the fixing. The five hour paint job becomes a twelve hour paintjob or you spend thirty hours on a twelve hour sculpt... and the final result is still compromised by that early mistake. This is not constructive and you're fighting against that logical piece of thought that has been nagging. Start again.
But we don't want to start again. It means going back over the same ground and, worse than that, we feel like we've failed or we're stupid. So we work extra time for an inferior result. Well, you know what? Learn to recognise when you're going to spend a huge amount of time fixing an only partially fixable problem and then suck it up. And throw the work away. Strip the mini or start the sculpt over (in the case of the sculpt keep the original as reference for what you did wrong and what you did right).
It's okay to just say 'screw it' and start over. I have done this today and I feel good about it. I spent around twelve hours on a major sculpt over the weekend and I'd made an error on it within the first ten minutes. It's not an error that would make the figure wrong but the end result would have been short of it's potential and that's not what I wanted from the sculpt. So I started over and I've learned. And the next version will be better.