One of the early CrossFit mantra's was "Unknown & Unknowable".
While its not so much the case these days, it's fun AND productive to leave some workouts in the dark until a big reveal.
The CrossFit Open still operates like this (as best it can), as do some event at the CF Games. In the gym we like to do it sometimes by keeping workouts off the internet until folks roll in the door.
One of the big points of functional fitness is taking the fitness you build in the gym out to the world, a place where a ton of unknown and unknowable things exist. You can't prepare for everything, sometimes you've got to dive in and figure out breathing later.