This is a joke ntended to illustrate the sometimes absurd oversimplification that has to be made to do certain calculations. An apple falls out of a tree from 20 feet off the ground, how long does it take to hit the ground. Well, what is the drag coefficient? Assume it’s a sphere. OK, what about the texture, the air temp, wind, is the ground level and flat, etc etc. And as the problems increase in complexity the number of variables increases exponentially. So your professor might tell you to "Assume it is a spherical cow of uniform density“.

Often these estimates are actually quite good and trying to account for all variables isn’t needed.

We did prohibition once already. The result was that all the little guys went out of business and the big guys ended up in positions to be the only guys. I wouldn’t discount that as being a possibility for weed.