I meant in terms of exercises and program layout. For instance, you are doing one thing and it works decently, but then you completely change it and it works even better. How would you know what it was that helped you so much? You would want to gradually shift your routine or add in certain exercises to see if they help you at all.
If you are doing a pre-written layout like WS4SB or 5/3/1 then you would want to follow it as written, but at some point you are still going to have to mix up some exercises to get past a plateau. Changing five of them may do the trick, but there is no way of knowing what helped most.