A painting has a life-cycle like any thing else. I know, I just blew your mind. But let's move beyond the painfully obvious and discuss the one step that all artists know is coming, and dread it. The teenage stage.
At some point after all the sketches and the color studies and the initial lay-in, your painting is old enough to develop a personality its own. Like any young one, your painting will make mistakes on the road to success. This is not all its fault, really, because growing pains are just that. Painful.
Like a teenager, it becomes unsightly, base coat colors in place of pimples, structure loss and color issues in place of awkward proportions. Like any parent who loved the younger, more cooperative painting, you may feel like giving up on it. But like any parent worth their salt, that is exactly the time that you must have patience. Some paintings may rebel a little too much, being angry and ignorant, and those paintings may need a stronger guiding hand.
The real strategy to dealing with a teenage painting is breathing. I recommend breathing at all times, but when especially frustrated with a muddy face or an offensive background, you must breath. Set the paintbrush down, think about happy trees and afros. Don't make your Rockwell into a Pollock with rash, angry brushstrokes.
My entire goal when painting, outside of making a flippin' sweet painting, is to get past the teenage stage as quickly as possible. At some point you will hate your painting and want to give up on it, almost every time. There are three things you can do to alleviate this pressure and bring your teenager into a respectable adult without your painting screaming "I hate you" and slamming doors.
The first thing I do is realize that my painting is in the teenage stage. At some point during painting, I can feel frustration building. It may not even be noticeable initially. You may feel antsy, like you want to stand up and walk around, like an itch in your mind. This is the teenage stage. Don't get up now, because if you do, you'll look at your painting after pacing and realize that it isn't the same young project you used to know and love.
Realize the beginning of this stage and stick it through. This brings me to the second step: continue according to plan. I really wanted to add some red into this hand once I got done with the sky, but now the sky is all crappy and I just want to start over (insert clenching fists here). Wrong move. You're done with the sky now. What was it you were going to do next? Put red into the hand. Be the mature one, and go about your painting as if nothing is going wrong. Inanimate objects always win an argument.
Finally, like I said before, breath. This isn't just a big long sigh with some temple rubbing, this is a very pro-active break. What do you mean by that? you ask. First off, don't interrupt. Secondly, I mean that when you look at your painting (set the brush down, Wild Bill) it may take considerable effort to remember how it looked in your mind's eye. Look at your painting, really assess it. Is that color right? No, but it's an OK undercoat.
Maybe certain parts of your painting do need scrubbed out. I realized just recently that the underdrawing for one of my paintings was inaccurate. I had to paint over several parts that I really liked. But if I let fear of never getting just that right brushstroke again keep me from correcting foundational errors, then I would have one beautifully flawed piece of work. My painting would never grow out of its teenage stage, and spend the rest of its days on the couch drinking 2-liters and playing video games in my basement.
So look at your painting in an honest critical and positive light. Again with the seeming oxymoron. You point out what is wrong, you look for what is broken, but after that, you look for how to fix it. And make sure to realize what is working well. Build a plan of attack that builds on what is already on the canvas, and be methodical about it. When you know what you're going to do, go back to step two. Carrying out this plan will have you antsy and unsure, and it's all about sticking to the plan.
There are no-hope paintings. If it's for a commission, disown it after you're done. If it's for you, I don't blame you for whatever happens. I have a few nice cowboy paintings that used to be orcs... And sometimes a painting will all fit together. The teenage stage takes half an hour before it's through, and somehow you never had to deal with that sinking feeling. Great! But for all those other times, keep this in mind. Hopefully your next rebellious painting won't have a life-cycle that ends on the pyre.