It is so easy to go into a round of golf expecting to play well, but then, it could be the first shot, or the fifth hole where it turns to shit. And when it does, the common mistake is to get frustrated, pissed, lose focus, patience, forget your routine, rush, and start giving up on your round. If you find yourself doing this, don't worry, it's very common, and the good news is, its fixable.
The fix isn't easy though. You need to understand when adversity hits on the course; you need to stay in your routine, no matter how bad it gets. Slow down your thinking and maybe even slow your swing. The round could be going to shit, but you need to remind yourself that you need to grind. Grinding is a quality of the top golfers in the world. It is the realization that you don't have it that day, but you will scratch out a respectable score. You are going to persevere through the challenge and make the most of your round. Even if you had your sights on a 76 that day, but you need to grind for an 84, just do it and never give up. That grind will build character, mental toughness and the more grinding experience you get during your rounds, the better you will become. You will actually become a deadly golfer because you will get to the point where you don't play your best, and grind and still win. That's what some of the best pros do.
Build a strong mentality to never give up by always reminding yourself that when things get tough, you got to double down on your focus and will to finish the round. You will encounter great growth as a player if you can be aware of this and be disciplined about it.