How do I know I don't suck?

Guys, it's one of those times. I know the key is persistence, and that hard work will eventually bring you sure success. I believe that.
But it's just been soooo looong. 
I need to just be whiny and self-indulgent today, if that's okay with you guys. You know how I feel, right? I have had this novel done for a while. I've been querying it for a while. Heck, I've been querying some of my short stories since I was a freshman in college. But the rejections keep piling in, and it feels like I have so little to show for all the effort.
I think my perspective is probably skewed here, and it probably isn't nearly as long, comparably, as it feels. Other writers much awesome than I have had to wait a lot longer than this for their success. Everybody has to put in the hours, that's just the way of it.
But after a while, the lack of success starts to wear on you and you start fearing that your book actually totally sucks, that you can't write, that you're a hack. I've been feeling like that lately. If my book was any good, shouldn't it have found success already? Part of me knows that's ridiculous, I mean, The Help, a completely fabulous  book, was submitted to fifty agents before it got accepted. That sort of helps, but it doesn't make me want to just be published already any less.
Rushing things is not a good idea either, I know that. If I really do suck then I definitely don't want to be out there until I suck less. On the other hand, I do believe in my characters and my story and I want them to be out in the world. But also, it's impossible to be objective about your own work, and what if you just suck?
Anyway. The thing to do when feeling this way is to do your best work on your current project, and that's what I'm trying to do. Hopefully it will just make success, when it does come, all the sweeter.
What do you do when confronted with these thoughts?
Sarah Allen