Most beginners and intermediate lifters try too many exercises with mediocre form. Mastering 5-6 compound movements (squat, deadlift, bench, row, overhead press, pull-up) outperforms 20 poorly-executed exercises.
Why this works
Form quality determines results. Bad form on 20 exercises produces bad outcomes across all of them. Good form on 6 produces dramatic results. Focus.
Spend 6 months mastering form on basics. Then add isolation work. Most plateaus come from poor compound form, not lack of fancy exercises.