I try to explore a little when I'm frustrated online, especially when I'm losing to the same person repeatedly. If I feel myself getting upset, I start really examining my play for any patterns or assumptions that I might be able to tear away to improve. And not via my usual subtle adjustments; I completely flip my playstyle on its head. A lot of the time, I then realize there was a good reason I was doing what I was doing, and I change back to my old tactics after a fight or two, but sometimes I discover a new technique that will help me put up a fight. Or other times I just confuse my opponent enough to amuse myself. Plus, when you're experimenting and learning, it gets your mind off the exact results of the match. It's not about I won or I lost, it's this strategy won or this strategy lost. Takes some pressure off.
As an Ike player with fairly poor shield reflexes, I find myself being forced to approach projectile users very frequently. So much so that I often get in the habit of rushing down everyone without any reserve. When I'm losing repeatedly and considering quitting, I try to catch things like that and switch my strategy completely. I'll try hanging back and forcing my opponent to approach, then I'll try to adapt to the resulting defensive play. Or I'll completely re-prioritize my moves, so that I generally forsake standard attacks for grabs, or I start playing risky and fish for more smash attacks, etc. Seeing some opponents react to a complete change of strategy 15 games into a match is hilarious.