I was listening to the radio and, as part of a discussion on something called Declinism, a psychologist said something like, "it's well established that people focus on the negative." He went on to explain that this impulse to focus on the negative comes from our primitive ancestors; if someone was on look out duty while the rest of the tribe were gathering food, there was no need to pay attention to the lookout saying, 'there's no lion coming', but if you didn't pay attention to the look out saying 'there's a lion coming', then you wouldn't be anybody's ancestor.
I see this in writing. Give someone 90% positive feedback, and they fret over the 10% that wasn't so good. Do a class exercise and focus only on what you didn't get 'right', rather than what you learned. Get turned down once, and decide there's no point in carrying on.
I've done all of these things. The last one - oh, the stupidity - in my early 20s I had an idea for a book and sent off what I thought was a non-fiction book proposal to a leading publisher. They wrote back saying it was a good idea, but asking for some more information. I took this as a rejection, and never replied. Durr.
I have learned to be a bit more positive, fortunately. Get a rejection? Statistically, it means you're nearer to acceptance. Get some negative feedback? Lucky you - you now know what to do to make your writing better. Get depressed by all the bad news about the economy, epublishing, copyright? Stop reading all those blog posts and articles and use the free time to do some writing instead.
It may sound a bit Pollyanna-ish/utterly nauseating, but you've got to have a reasonably positive outlook and enjoy the journey or else writing will simply make you miserable. And no one wants that.