Pick two

I’ve always liked the old designer’s adage of “good, fast, or cheap, pick two”. That is, a project can be completed quickly, it can be done cheap, and it can be done well, but you need to choose which two of those you want. If you want a good project done quickly, it’s gonna be expensive. Fast and cheap? It’s gonna suck. In his talk at SXSW, Jason Fried outlined another pick two scenario clients need to be aware of: “fixed scope, fixed timeframe, or fixed budget”. Here are some more variations:

Elegant, documented, on time.
Privacy, accuracy, security.
Have fun, do good, stay out of trouble.
Study, socialize, sleep.
Diverse, free, equal.
Fast, efficient, useful.
Cheap, healthy, tasty.
Secure, usable, affordable.
Short, memorable, unique.
Cheap, light, strong.

In considering these sets of trade-offs — accepting that they are cliches and therefore both overly general but also fairly accurate across a range of diverse situations — two questions come to mind.

• Why is “pick two out of three” the rule? Why not “one out of two” or “four out of six”? Or is “pick two out of three” just a cultural assumption?
• Is there some underlying scientific or economic relationship here? What do the situations in which “pick two” logic applies have in common? In clumsily casting about for an appropriate explanation/metaphor, I considered the triangle (all interior angles add up to 180 degrees), thermodynamics and entropy, Boyle’s Law, Hooke’s Law, the Heisenberg Uncertainty Principle (although that’s a “one out of two” thing), Ohm’s Law, and Newton’s Second Law of Motion, but none seem to fit well.

I’ve poked around a bit online looking for discussions of “pick two” systems and have come up empty. Anyone have any ideas about this? Any good resources to check out? Something tells me I’m missing something obvious here. (Or onto something interesting.)