Originally published six years ago, the article "Zatsiorsky, Scaling, and Power" by Jon Gilson (founder of Again Faster and former member of the CrossFit HQ Seminar Staff) is as useful today as it was back in 2010.  Check it out:

You could struggle like a rocket trying to take off on regular unleaded, or you could actually get stronger.
You’re the kid who saw one phenom go from high school straight to the Major Leagues, and figured “What the hell?  If that skinny punk can do it, so can I.”  Attention, achievement, some sliver of recognition, nothing less will do.
You’re Rx’d.  You made the Major League jump. Except, you really, really shouldn’t have, and now you’re striking out.  Slow your roll, tee ball slugger.
It’s okay.  I did the same thing, and if I don’t admit it, the pot would definitely be calling the kettle another piece of kitchen equipment.  Learn from my stupidity.
This is not what we meant.The whole point of our sport is power output: do more work faster.  Intrinsic in this little missive is “faster”, but every guy secretly wants to be bigger and stronger, and figures that what we actually meant was “heavier”.
It comes down to simple physics: power is the product of speed and strength.  Too much of either (without the other) will result in extremely blunted power.
Imagine speed and strength on the see-saw together, and strength is the fat kid.  The really fat kid.  In fact, he outweighs speed by a factor of ten.  The see-saw stays stuck, and no one has fun at recess.  Escaping my metaphor, if the load is too large and speed is too small, power is zip, much like multiplying by zero always gets you zero.
Now, imagine speed and strength are balanced, each kid weighing about the same.  This parity allows them to act in concert with each other, and the see-saw really flies.  We get power.
“Heavier” isn’t the answer.  Balance is the answer.
On page six in The Science and Practice of Strength Training, author Vladimir Zatsiorsky posits that maximal power output occurs at approximately 30% of maximal velocity and 50% of maximal load.  I’m in love with page six, and simultaneously dumbfounded by its mathematical exactitude.
Applied to CrossFit and our never ending pursuit of power, this unforgettable page states that we’re looking for a load that you can move with 30% speed, one that tends to occur somewhere around your 50% of one-rep maximum. 
Of course, CrossFit won’t ask you to move the bar once, but perhaps ten or twenty or fifty times.  To maximize your power across this broad spectrum of work, you’ll want to load to less than 50% 1RM, and continue to try to move the hell out of the bar.
Holy shit.  A formula for scaling.
For too long, we’ve focused on strength bias this and power animal super athlete that, when this entire program is predicated on power. Stop thinking of scaling as something to keep Grandma in the game.  We scale to the physical and psychological tolerance of the athlete for one reason: it enables the individual to produce as much power as possible.
Following Zatsiorsky’s formula, if you can’t thruster at least 190 pounds, you shouldn’t be doing “Fran” with 95.  If you can’t clean and jerk 270, don’t do “Grace” with 135. You’re blunting your power output.  Scale that weight down; it will make you more powerful.
I did not just tell you to abandon heavy weights. In fact, I want you to lift heavy.  A lot.  Just not in the middle of your WOD. 
If you increase your 1RM, through any number of methods, your 50% 1RM will go up as well, and you’ll climb into the Rx’d echelon via this prescription.  You thruster 150, you do “Fran” at 75 pounds or less.  You thruster 200, welcome to the Big Leagues.  
In other words, don’t strength bias your WODs—strength bias your strength, and scale your WODs to your current strength level.
Proof? Take a look at the strongest men in the world, not by fiat, but by actual numbers lifted, the gargantuan boys of Westside Barbell.  Their program regularly calls for moving 50% 1RM as fast as possible.  In fact, it was a conversation with Louie Simmons, the founder of the Westside Method and its Dynamic Effort Days, that persuaded me to pick up a copy of The Science and Practice of Strength Training in the first place.
I’m sure he’d be disappointed I never made it past page six, but I bet he’d love it if you stopped trying to do Fran with 65% of your 1RM.
The successful implementation of scaling demands a simple recognition: there are an infinite number of weights that can be loaded on a barbell, and every one must be removed from ego and firmly affixed to power.  When this mental shift occurs, we’ll get more powerful athletes, guaranteed.
-Jon Gilson

This article is a great segue into Tuesday's workout below, which was a CrossFit.com main site WOD from the Fall of 2014.  The WOD looks so simple on paper - it starts out harmlessly in terms of loading - and some athletes may be convinced that they can start at the Rx weight of 75/65 lbs (as we have scaled it) and have no problems getting into the 20+, 25+, or even 30+ minute range.  Here is where understanding 1) what the intended stimulus of the workout is; 2) how your current strength and fitness levels fit into that intended stimulus; and 3) how best to scale & approach the workout in order to get the highest possible power output and overall benefit can greatly improve the effectiveness of the workout and the positive adaptation you glean from doing it at an appropriate sequence of loading. 

Here are two former CrossFit Games athletes, and still some of the fittest guys out there, doing the WOD starting at 75 lbs.  Their final scores were 25 minutes (Pat Barber) and 35 minutes + 4 reps (Wes Piatt): 

WOD for 06-14-16:

With a Continuously Running Clock...

Complete 5 Thrusters Every Minute:

0:00 - 5:00 use 75/65 lbs

5:00 - 10:00 use 95/75 lbs

10:00 - 15:00 use 115/85 lbs

15:00 - 20:00 use 135/95 lbs

Etc...

Continue adding 20/10 lbs every 5 minutes for as long as you are able.

Score is minutes completed plus any reps in your final partial minute.