I don't think that I have completed one single painting where I haven't thought somewhere in the process that I would like to throw it out the window, burn it or banish it to a cupboard never to see the light of day again.
I think that this is an important part of the painting process.
The only time when this actually affects the painting negatively is if you carry on painting when you are too tired and have reached the 'throw it out the window' point, or if you are angry at it and you continue to paint. If you get to this point it is important to take a longish break from that piece. By long-ish I could mean a couple of hours, overnight or a week depending on when your deadline is.
Normally a couple of hours does it.
I think that when we get into the mentality of 'I never want to see this again ever, its the worst thing I have ever done' we aren't really looking at the painting, we are just judging ourselves. Frustration can be blinding, so its important to take time out and gain your sight again.
Currently I'm at the throw it out the window phase with a painting of a house plant. I don't think I have the patience for painting plants. But to be honest, I'm just expecting too much of myself in too small an amount of time. Of course I'm not going to be able to paint like some of the amazing botanical artists that there are out there... when i have hardly drawn/painted any plants in full detail ever!
Of course it is going to be tough, and of course it is going to take me a lot longer to complete it than if I was painting an animal in high detail (seeing as I have more experience painting them) Plants should not be underestimated. no No NO. Far more complex on the outside than a lot of animals... but perhaps that is because I'm used to looking at living things that move.
Anyway. I will consider this a work in progress and move onto something new for the time being.