I would say alter your training regimen according to how your body reacts. for example if your working out 4 days a week and stop seeing large results you probably have reached a plateau and need to change your training schedule to add day or so more per week or just change the exercises you are doing for each muscle group. this could in turn shock your muscles out of their ordinary routine and keep them guessing what you will hit them with next.
Alternatively if you are going 5-6 days per week and don't feel like your getting enough out of your muscles think of how much your training each muscle. Is your chest day really just chest or are you indirectly working your triceps and delts as well. In this case you might need to combine multiple workouts to keep your muscles guessing. Also be careful not to overtrain, certain body parts are working for you multiple times per week just to complete other workouts. example would be triceps are worked chest day, biceps are worked back day...
Mainly my point is (without babbling on another tangent) experiment with different training regimens and figure out what is going to work best for you. Some guys like push/pull, some like upper body/lower body, some like split so on and so on. Hope this helps clear some things up. If not I might have inadvertantly confused you even more.
