Good point (which  is essential to keep growing but everybody seems to ignore). It is not even just to confuse muscles. You can't lift heavy everytime, too hard on joints.

Good job Scooby

personally what i do; i lift heavy weights when i do biceps and it allows me to do 8 reps with good form.  then at the end of my workout, i do 21's with a light barbell; it gives me a great pump and i think it confuses/shocks my muscles when i go from heavy 8 reps to light 21 reps.  it's great.   

Guys, notice that the video is not about doing 21s at the end of biceps workout, it is about alternating heavy and light workout SESSIONS. I don't understand why people love this 21s so much, any exercise will have the same effect if you do consecutive 7 partial (bottom), 7 partial (top) amd 7 full ROM, this doesn't apply to bicep curls only. It's lactic acid, you need to increase your tolerance towards it if you want more endurance, but you don't need that "pump" or "burn" for hypertrophy. 21s can be done in a light session, or as a "burnout method", in which you work on maximal strength (high weight/low reps) for a few sets and then one sub-maximal set (low weight/high reps). This can work if done every once in a while, but I don't believe it's the best thing to do on a regular basis, since it has shortcomings such as higher risk of absolute CNS fatigue. I also believe you need to focus on increasing one or two strength qualities in a session. I suggest focusing on maximal strength a few session and nothing more, AND shocking muscles during a single sesison. It's not good to work on excessive parameters and accomplish everything in one session. That's not this video recommends anyway.

I've been changing my routines like changing clothes over the last 9 months. High reps - low reps - isolation - compound - machine - freewweight - 5 days rest - overtrain purposely..... and sometimes I thought that would be the best because my muscle will be "confuse" and always make gain.
But now that I really think about it, every routine or approach have its benefit, but the marginal benefit only come to the Maximal point if you keep at it for a certain amount of time. So if I can't keep up with one approach for more than 1 week, it means I can only get the early marginal benefits of it. Of course I wouldn't reach plateau by switching, but I can't have maximum benefit of any approach whatsoever.
Here's how the graph look like (I know that you all already know this)

         /\ -maximal point
      /      \
   /            \
/-start point   \
                      \ 
                         \______________ -plateau
(marginal benefit)

So in my opinion, mixing up is a great thing, but don't be over hype about it and start changing your approach like crazy. Just like Scooby says, 1 in a months to do high reps is great. Or I would do the 3 or 6 week cycle, one day of high reps every 3 weeks low reps.

Honestly, I am embarrassed about this video.  I have been really busy and the main two videos I am working on next (teen workout and Alcohol/bodybuilding) are taking a lot of research to get right and wont be ready for awhile.  I wanted to put out something in the meantime but I didnt take the time to script it out (big mistake).  The video kinda gets the points across but not clearly and some of the most important points I wanted to make got lost.  I need to realize my limitations, that I will never be one of those people who can grab the microphone and chat away coherently - Anderson Cooper can relax now, I'm not after his job. 

Points this video was supposted to convey:
  1) mix up your workouts
  2) Why?
       a) more/faster gains
       b) reduced joint wear and injury potential

On point 2b I failed, it was so obvious to me that it didnt occur to me to emphasize it. 

Anyway, every once in awhile there is a clunker. 

Mixing it up, I never repeat the same routine. I may do the same exercise or two, but I try to use different workout's each time for each muscle. Think this is a good idea? I figured it would be hard to get muscle memory if the workout routine is never the same.

this has probably come up before somewhere else, but i'm gonna ask it here because it seems relevant to me:

is the rep number Scooby does in this workout good? i mean going as heavy as 3 sets of only 3 reps, for building mass? or is it better to do 3 sets of 5-8?