To be honest fellahs, the vast majority of gym-goers don't stick to any one routine or diet for 6 weeks, let alone 6 months.
And if they do stick to the routine for 6 weeks, then they do not progress it. Looking at their programme cards we see that they're using the same weights, reps and sets for the whole time.
Usually after 4-8 weeks they either quit having a routine altogether and just wander randomly from one favourite exercise to another, or else they get a new routine from one of the enter-trainers.
Last night I was talking to another trainer, I asked, "Who's giving the rehab-style exercises out?"
"Like what?"
"Like that girl squatting on an inverted bosu ball."
"Oh her, I gave her that exercise."
"Does she have stability issues? Some injury being rehabbed?"
"No."
"Then what's the purpose of the exercise? What is she trying to achieve?"
"She gets bored easily, likes new stuff."
And indeed some people actually believe that doing a heap of different exercises will stimulate more change than simply doing a few exercises and progressing in them. They believe this without having ever actually met anyone for whom it worked.
Frankly I'd be impressed by any regular gym-goer who could stick to a single routine for a whole 6 months.