When you lose a point, it is not because you hit that forehand long, or because your opponent hit a winner.
Unforced errors and winners are determined long before they actually happen.
All your opponent has to do is create an opening, cause you some slight discomfort. And build on it. Push you onto your back foot. Each ball seems further away and you scramble to keep up.
When you lose, you feel like you should have run faster, tried harder.
Recognize when the first opening was created. And close it.
Or better yet, create the opening yourself.