Losing, but maybe not the way you'd think.
Letting my game evolve has sometimes required taking a leap of faith and completely embracing something new. Some years ago when I retooled my ground strokes, I had to decide to hit my updated one-handed backhand no matter what, even though it wasn't initially very good. I had to learn to trust it during competition, but that meant taking some lumps for a little while. Being okay with losing over the short term let me improve instead of clinging to bad habits.
Losing in a situation where we're using our best stuff can also help with improvement, but that requires being honest with ourselves and taking a realistic inventory. Example: one great first serve shouldn't distract us from the hard truth that we badly missed perhaps eight or ten first serves going for that hero shot. All that does is hand an opponent too many looks at second serves.
Losing also doesn't mean we have to hate ourselves. With a little awareness, a loss can offer a sober progress report. If nothing else, it should be easy to get a sense of how many errors vs. winners we're racking up against a decent opponent.
In terms of basic technique, I'll offer that the vast majority of recreational competitive players can get faster with their setup or stroke preparation. This boils down to using a deliberate split step as the opponent hits the ball and then aggressively bursting to either side with both footwork and a shoulder turn to arrive more quickly at the hitting area ready to swing... EVERY time. When a player can learn to rush his/her shot preparation as part of their basic routine, it becomes much easier to execute an unrushed stroke more often.