Variety vs. Mastery...
Even most experienced lifters are still beginners because too many people emphasize variety over mastery. If you can't deadlift twice your bodyweight or power clean press and front squat your bodyweight you are too weak for most strength and conditioning progressions. I say this not out of ego but out of regard for preventing injury. If you can not meet these strength standards I can predict with some accuracy what your next injury will be based on your weakest lift.
Too many people believe in randomness or variety as a virtue. It is not. Exercise is movement for movement's sake. Training is movement to elicit a specific response. Most of our goals are specific, not random. If you wish to get better at a specific parameter you must dedicate your training toward's effecting that parameter. Radical idea I know.
Overemphasis on exercise variety is the manifesting of mental laziness, not hard work. If you want to get better master the basics before you adding variety.