I tried once or twice to edit articles but was quickly rejected by editors that usually believe they sort of "own" the content. I've quickly become demotivated as explained in the analysis and never contributed again. Another problem is that when you think you've made an important and useful update you're never sure when someone will roll it back. Some are spending a very big chunk of their time to make sure articles…
I have learned that in order to actually contribute to Wikipedia, you have to treat it less like a collaboration and more like a battle. You can't just contribute and consider it done. You have to be prepare to fight your way through, engage in edit wars, learn about the battlefield (the bureaucracy, the article sourcing) and in the end, if you fight long enough, you usually win. You have to repeatedly, over and over…
And this is why only fundamentalists and paid editors edit Wikipedia. I spent days with such battles on a certain Wikipedia page only to have one "senior" editor come around and essentially say that I was wrong (no explanation given) and revert the changes. It's a completely useless waste of time. :)