How to change General thought processes during chess play?

Hi there! I was wondering how I could change my thought processes when I am playing chess. Often times I make the same chess mistakes over and over again. Mostly it is that I am very sharp for for instance 30 moves and then I am suddenly too lazy/tired to be very sharp at move 31.

Is this a concentration problem or a thought process problem? And how can I conquer this? Thanks for your answers in advance

Try a bag of Ice over your head

Anyone serious?

umm.read bookS?

get some air

Self-flagellation

ive had the same issues and have improved vastly by simply using my time effectively and trying to think deeply and not blunder in the later moves - i think when you get to a certain level, people are good tactically and positionally but they make small mistakes in the way you described - so it becomes a battle of will and making progress while not blundering, especially later in the game (i would also say after move 30)

the way i combat it is just to be aware of how much of an issue it is and to make sure i use all my time and not move on instinct (since my intuition sucks)

I have that problem too, I often build up a good position in the opening and then I screw it up in the middle/endgame. Maybe it would help to learn more openings so you don´t have to think so much in the first moves.