Losing sucks, but it never affects me. I can easily laugh it off because when I play, I'm thinking about long term and not worried about short term variance/bad luck that's bound to happen.
At a casino the other day, I was up about $400 at 1/2, bought in for $100. Got AA for the 2nd time in about 20 hands, first time I got no action. 2nd time, I raise PF, got re-raised by a stack of ~$150, one cold caller, I shove, ~$150 calls, cold caller folds. ~$400+ in the pot. I flip over AA, he flips over 66. Flops a 6 and takes the pot.
The entire time, I'm just laughing and congratulate him on his win. I think we even hi-5...and people were asking how I was so happy to lose with AA? And it's because beats like this don't affect me. The fact that he was risking 75BBs preflop with just 66 is great news to me because I know I can stack him most of the time with my big hands. If he over values 66, he's definitely over valuing hands like AX suited, A/10, KQs, KJ, mid pairs. I have just pick a hand that crushes his range and get paid off. Again, his short term luck got the best of me, but in the long run, I'm making so much money off of him.
-If you're making +EV moves when you're a favorite to win, you'll win more in the long run than you'll lose.
-Focus on the long run with poker instead of short term results. You get KK AIPF, someone calls with A/x unsuited and snags an ace. Maybe it was for 100+ BBs, your tournament life, whatever. It sucks, but seeing as you're a 70% favorite to win the hand, you made the right move and got unlucky. Unlucky is short term, skill goes a long way.
-How much did you really lose and how much is the loss really affecting you? If you're playing 200NL and losing $200 isn't that big of a deal-as in, it's not going to affect your life in a severe way because you still have savings, you can pay for bills, take care of life, etc. Then don't let that single buy-in get you because it's going to happen. You should also be playing within your BR for bad beats that do happen.
Again, think long term. In the same example above, lets say effective stacks are $200 (100BBs), at 70% to win, you're expected to win $1400 vs losing $600, for an $800 profit in the long run for every 10x this hand happens.
-Keep mental tabs on those people who are playing bad. Trust me, they'll pay you off a lot more than you pay them.