What separates tennis players are seldom their technique, but how good they are at consistently playing close to what they already own in matches.
We have to remember that Tennis is an extremely complex sport where the amount of skills you need to master is huge. Simply think about the forehand & how you need to be able to hit it at waist-, hip- & shoulder height with different spins & court positioning in both offensive, neutral & defensive rallies. AND that is just the forehand then there are all of the other strokes & on top of all the strokes/skills you need to master you have an opponent! …and the only job of your opponent is to make life miserable for you on court.
In other words thinking that you will be able to perform on the same level as your best ever performance every time you step on to the tennis court is simply UNREALISTIC.
Instead it’s about trying to figure out a way to pull through with what you have got on the specific day whether that is 70 %, 75 % or maybe 80 % of your best ever performance on a good day.