Why are exec and run so confusing?

DRANK

Originally posted on the Spinel blog. While working on rv, there’s a specific question that has come up over and over again, in many different forms. In the simplest possible form, it boils down to: What is the difference between rv exec and rv run? Why have both? We haven’t finished implementing either rv exec or rv run yet, but every time one or the other comes up in a conversation, everything instantly becomes more confusing.