I'm having to back track on my current big painting, which means it won't be done in remotely the same time frame as I was planning on. I hate that. There's part of me that wants to move forward and just finish it, but it's REALLY not working out the way I expected. There's two opposite lessons I have learned from my paintings when this happens. Sometimes, it's right to just move forward and finish it, if I realize that there's nothing left I can do that would improve it greatly. Other times, like now, it's better for me to admit my mistakes and let go of my "schedule" and a lot of the work I've completed so far. It's frustrating, because I feel like days and weeks have just been lost as I redo much of what took me so long to complete. This generally happens when I strike out and try something different, using techniques (or colors or whatever) that I'm not as comfortable with. I have to learn how to make the painting as I'm making it.
The good news is, this process has always resulted in paintings that were ultimately superior than some of my other work. It's like you can tell just by looking at it that I spent an insane amount of extra time doing it.
So... at least there's that.