First, a tangent. Actually, this whole post is a tangent.
Graduate school was the hardest thing I ever did. It wasn't just intellectually challenging, it was emotionally devastating. I worked in a great lab with great people and my supervisor was arguably the nicest human being on the face of the Earth, but I was confronted daily with the limits of my own abilities. And that experience was nine pleasing shades of hell on my ego. I was miserable.
But there's one thing I did during that time that I'm proud of. I owned my failures.
It's fairly common to witness frustrated writers getting angry at the query system--at the "gatekeepers" of publishing who bar them from the industry based on a whim and a one-page letter. I'm not going to discuss whether these writers have a valid point; I'm only going to note that this isn't a useful mindset. For one thing, it's not healthy to get angry at something you can't change, and on a deeper level, that mindset will cause you to miss opportunities for future success.
Events (and sometimes people) will always get in the way of you reaching a difficult goal. If you suffer a failure, you may be completely correct in blaming outside circumstances for it.
However, you can't stop there. You shouldn't think, "It's their fault," and then hop in the hot tub of sulk. You have to go one step farther if you want a better chance of reaching your goal on the next attempt.
That one step consists of owning every part of the failure that you can. Don't blame yourself for the things you really can't control, but everything you can accept responsibility for? Humbly nod and say, "Yup. That part was my doing." The query letter? Own it. Sample pages? Own them. The presentation, the manuscript, the way you spelled someone's name? Own all that. It's not relevant whether the person receiving the query should have been more forgiving of your naivety--own those parts that you were responsible for.
The reason why is simple: if you blame others for a failure, then by that logic, there's nothing you can do to make things better. You're impotent; you're helpless; you're irrevocably held down by The Man.
However, if you accept responsibility for every part of the failure that you can, then you've admitted to yourself there's something you can do--something you can improve on for next time. You've given yourself the means to keep fighting. You can now concentrate your energy on everything you can change, rather than everything you can't.
Blaming your failures on outside obstacles is always easier on the ego, but please decide which is more important to you--your goals or your ego? In order to learn from your failure, you have to own it.