Face it.. if you want to be successful at anything, discipline and consistency are mandatory.
You've got to be willing to work hard week in and week out, and put forth the effort even on those days when you'd rather stay at home, lie on the couch and relax.
The saying goes: "80% of success is showing up", and for the most part I'd say that's true.
Building muscle is basically no different.
You've got to stay tight to your workout schedule and get yourself into the gym even when it's the last thing on your mind. If you want to gain muscle size and strength as quickly as possible, you should never, ever miss a workout..
Or should you?
Well actually here's the thing..
Yes, consistency is important. Yes, you should be sticking to your workout schedule the vast majority of the time. Yes, simply bailing on the gym out of pure laziness is not acceptable.
However, to get a point across, I would like to bring up a quote from the late Mike Mentzer. He said: "Rituals have nothing to do with science".
What you need to keep in mind is that the human body is an extremely complex biological "machine", and that not every single workout and recovery period is identical.
In other words, just because your schedule states that you must train on days X, Y and Z doesn't necessarily mean that this will always be the optimal pattern every single week of the year.
If you wake up on a training day and your muscles still ache, you feel physically tired and your regular motivation to train just feels like it has been zapped away... don't you think your body just might be trying to tell you something?