How do you deal with it?
I personally find it increasingly difficult to be polite about it - especially as I grow older.
Afterward, I take the time to mourn and process the rejection. It sucks and that's very human. I've been rejected more times than I can count, and at times, I was overly confident that a job was going to be mine during the interviews.
I've learned to keep going and put myself out there over and over regardless of what happens. I'm doing this right now for a job that's really calling me, like one of those 'I don't want to wake up at 60 with regret if I don't at least try.' You miss 100% of the shots you don't take.
That being said, had I been at the previous startup I had joined as an intern, I might have earned been earning more and it still feels bad from time to time. But having a stable job and stuff to focus on helps keep me distracted.
I was getting pretty bitter about the whole thing, seeing people who could talk a good game in jobs they couldn't do properly, certainly not as good as I could.
I realised it was all a big game though and eventually played it good enough to move to a job I wanted. Much as I hated playing the game, it was that or quit.
It still affects me in some ways but not particularly in my career (e.g. I am not a great salesperson but I feel about cold calls the way Brer Rabbit feels about being thrown in the Brer Patch.)
Overall it has gotten better as I have gotten older and I expect that to continue.
You don’t know if the company actually thought your performance was bad or they just hired internally or randomly chose someone else.
And even if you know your performance was bad, that doesn’t mean you are a failure. Everybody makes mistakes and everybody has flaws, and truly understanding and acknowledging your strengths and weaknesses is one of the best abilities you can have.