Scarcity mindset is thinking that however you achieved a degree of success in something, must be the best way to do it--there's no possible better way.
For example: athlete bench presses 165 with elbows flared. "Okay not bad, but if you bring your elbows in and tuck, that’ll be even stronger." Athlete replies, "But I got the lift". He cannot see that his success with 165 was only because ANYONE doing ANY type of technique and training can bench 165. He fails to absorb the lesson that even though his lift of 165 was successful, there’s better more efficient ways to perform the exercise. So ultimately he’s then unable to ever handle actual big weights in the bench.
Whether bench pressing or out on the field, athletes low level successes, and for the very talented, higher level, is often simply because of their genetic gifting, not because of anything they’re actually doing correctly. Those who can sustain success through the more competitive levels of sport know that processes must be evaluated constantly, in order to improve. MLB great Orel Hershisher said the difference in his journey from mediocre pitcher to NL MVP was learning to evaluate his outings not off how many runs he gave up, or even whether he won or lost; but critically examining how effective he ACTUALLY was: did he pipe a fastball a guy should’ve hit a mile, but instead popped up? Was his changeup flat but guys still happened to make weak contact with it that day? It takes a humble, hungry mind to objectively evaluate ourselves and constantly seek better ways in order to improve. Small minds say, "well I hit the lift" "well he still popped up" "well I'm still making money". Never forget Barry Bonds hit 37 HR and was NL MVP, and still realized being EVEN BIGGER would make him better. And that resulted in 73 HR, the record.