Losing deliberately
When I was younger, I noticed that losing in games, especially over and over again, could be an unpleasant experience for some people — and they don't react well in those situations. So, at some point, I started losing deliberately at games that I was good at because I was afraid that people might stop playing with me.
Over time, the act of losing deliberately became more refined. For games that I'm statistically a lot better at than those I play with, I'd teeter on the edge of barely losing and just winning to create tension and a false sense of competitiveness — all so that I didn't have to deal with people reacting badly to losing. Unfortunately, for games that I'm new to or not very good at, I would also not take them seriously for similar reasons.
What I didn't know and should have realised sooner was that people who always react badly to losing games are called sore losers, and the best thing to do with them is simply to not play with them again; otherwise, everyone loses in the long run.