It's amazing to me exactly how hard instances can be. Not the mobs, but the group. We've all been in ugh-PUGs before. Some players don't understand how to use their class or play nicely in an instance. That's only on regular dungeons; heroics have their own set of potential disasters. Sometimes you just have to give up.
Putting a group together for instance can be extremely difficult, and sometimes you have to take what you can get. While there are many excellent tanks out there, the shortage on my server makes for slim pickings. Folks who think that pulling aggro off the tank is an honor make up another problem. I am occasionally guilty of trying to heal and DPS at the same time. I'll admit to causing a wipe or two because of it.
I had a Steam Vaults run once where the Mage insisted on tanking and the Hunter showed up with four empty gear slots. We didn't survive the second pull. After the second try, I was out of there. I try my best to keep it together, but sometimes discretion s the better part of valor.
So what happens when the DPS are dopes, the tank tanks, and the healer is heel? How many wipes does it take you to give up on an instance?