If you keep losing to the same person, stop trying harder and start studying how they win.

Trying harder repeats the same approach with more effort behind it, which gets you a closer version of the same loss. If one person beats you consistently, the gap is in method rather than intensity. They are doing something specific and repeatable, and it is visible if you stop competing long enough to watch it.

Next time you play them, give up on winning that match and spend it collecting information. What do they do first, where do you start losing, what do they do when they are behind. Then change one thing in your own approach and try again.