this might not work for everyone, but what helped me is to understand what to expect when i play mtts and, therefore, it's not a surprise.
my itm is ~20%, which means i will cash in 20/100 mtts i play. while going 80 mtts without a significant cash would suck, it's not impossible. and i've accepted that.
understanding
equity is big as well. once i understood my equity vs opponent(s) equity, in any situation, that made those losses easier to handle and got to the point where i'm not phased by it because it's all simple numbers. it's also important that equity differs in all-in preflop situations and post flop situations.
once i understood and accept how this workout in the long term, i stopped being bothered by anything. in fact, it's really hard for me to see anything as a bad beat. not saying there aren't such things, but i think it's more of a matter of perspective.
while someone might see losing with ak vs 34o when it's all in preflop and the opponent hits river a gutshot straight might see it as a bad beat as a 92% favorite, i see it as my opponent's 34% preflop equity getting there. or even if my opponent does call a turn bet/shove with 8% equity and hits, i don't see it as a bad beat. it see it as i'm winning 92% of the time. just because i lost in this particular hand doesn't matter in the long term. a) i'm not going to win every and and b) i don't need to win every hand. it's all about you +ev decision making and not the results. besides, i'm happy to lose to a 4 outer 8% of the time on the river.