Fitness is 90% mental, 10% ability.
You are what you think you are in your workouts. If you treat yourself in your mind like a delicate, injured, aging creature then that's what your body will turn into.
In high school I ran cross country at a competitive level but frankly I was never the leader of the pack. For a distance runner I'm way too muscular and not all that leggy. I loved running because of the mental toughness it taught me. Running is such a mind game. I think it's really the toughest mental sport there is. Really there's just you and your legs, no props, toys that are better than others, nothing!
Running taught me how to talk nicely to myself during a workout. I learned that the more I mocked, yelled, made fun of myself on the inside the worse my workout results were. During my own workouts now I actually cheer myself on (sometimes out loud!) and this seriously transformed my training.
If you want to get faster, stronger, better at your workouts then you've got to be nicer to yourselves. I see this all of the time with a few clients, they literally beat themselves up inside during a workout. It crushes me to see this. As a trainer I can see mental fitness at a bird's eye level. If someone consistently stops on the last rep usually it's because they are telling themselves they can't do it, it's too hard, they never finish. Beware: THIS DRIVES ME CRAZY. Because I know you can do it and I want you to believe in yourselves. Having a trainer to boss you around and force those reps out of you is great but it's a luxury and really I can't be with you every step of the way every single day. You need to own it and develop some mental toughness before you are going to see any sign of physical improvement. Strong mind = strong muscle.
I suggest starting with a few positives to think about, even just repeating something like "you've got this", "you're awesome" … whatever it is just look for the positives and cheer yourself on. It will feel weird at first but this really does work!! Go you!! Wooo hoooo!!