I don't think feeling sad is silly at all. Three rejections within 24 hours here. I'm not sad, though, more like frustrated, and I think I finally figured out what gets to me.
You can say: I lost because the other guy ran faster than me. I lost because his queen ate my king. I lost because I couldn't solve that math problem in ten minutes. You can analyze your situation, find the precise reason, and then start looking for the way to improve your performance.
Here, once you move past the basic mistakes, you don't really know why you are losing. Another guy's query seems to be worse than yours, yet he's getting requests and you don't. There are better books than yours, yet they fail utterly when it comes to getting an agent's attention. Even if people are nice enough to write you little notes, you can't always rely on them. One agent says she loves your style, another says your style is awkward. One agent loves your character and hates your plot, another one loves your plot, but can't connect to your characters. The book you thought was your best one doesn't get a single yes, and then something you scribbled as a way to entertain yourself gathers two full requests in the first week of querying. Experienced agent sells your book to a big publisher in a great deal, and then it flops like rotten fish. No one can say anything for sure.
And sometimes it's just personal differences. A recent example: a very nice agent says, I love your plot, but unfortunately your book itself just didn't click with me, it's too visual and it has too much action. Eh, I think, those were supposed to be good things, no? But then I read a book the agent reportedly loved and called "high octane action"... and what I'm reading is a slow, introspective book that has no action whatsoever until chapter twenty or so. It wasn't a bad book, but "high octane" is the last thing I'd call it.
It's just so chaotic and irrational.