I was discussing the concept of loss and gain with a neurologist recently and he explained that the human brain reacts more actively to loss than it does gain. So for example, if someone said, "I saw you dropped a $20 bill on the ground down the hall, you can go get it though" versus "There's a $20 down the hall that's free to take if you go and get it", a human is more likely to reclaim the lost $20 game. Similarly in Splatoon, we tend to have a bigger reaction when we lose than when we win.
I think we react that way because of a mixture of two factors. One is time lost, as we can feel like we wasted our time on a lost game and want to "make it up". Another element is pride, which we feel is hurt if we go out on a loss. The problem with this is that we're quietly telling ourselves that we can only have fun with Splatoon when we win. That's not a good way to look at Splatoon, and I suffered from this for a long time. These days, I have learned that it can still be fun if you lose a game, especially if you feel like you played well and even more so if it was a close game. I would rather lose a Turf War 43% to 46% than stomp a team with no effort for 64% to 29%.