To add, getting fitter is a simple concept but not always easy in practice. Do progressively more work over a specified time period. If you’re ever at a point where you start to fail workouts, the mind games start as we try to figure out why it happened. But a failure means typically workload was not met, and thus progressive overload will probably not happen for that micro cycle but may still be there for the macro cycle. This is why it is almost always better to err on the side of too easy as yiu can slowly ratchet up the training load.
The refusal of some here to see that if the metric to set your workouts isn’t based on your actual abilities then the goals of the prescribed workouts have then changed is just holding yourself back.