Many people can only get so strong.
I have seen it forever.
A lifter can get strong, strong compared to regular people, like a 350 bench, a 500 squat, 550 deadlift. But they can't get to the 800 squat, 700 deadlift, 500 bench because they actually get scared. Scared of doing what it takes. It's fucking hard as hell to get that strong. Nosebleeds, ripped muscles, ears ringing, total commitment to it. Walk before you run, but preferably sit. All focus on the task. Until the lifter is ready to say screw how it feels, screw being tired, screw a relationship, it's gonna be damn tough to reach some crazy numbers. Never make excuses, and no missed reps, ever. Ask someone who has been there. It is never a part-time thing, always full-time.
Strong but not really strong.