What do I mean?
Pick any exercise you do every time you go the gym. Is it the bench press, chest press, leg curl, leg extension, arm curl, squat, etc? How many reps and sets do you do? Where did you come up with that number? How much rest and weight do you use? Why?
John (45 years old) goes to the gym every morning at 5 and heads right for the chest press machine and does his circuit. He has been doing 12 reps and 3 sets since high school and has been doing pretty much the same workout since he can remember. Another variable is that he stops and talks to his friends for minutes at a time between exercises which is one of the reason why he still goes to the gym...to be social.