Glen Whitman has been compiling a list of The Two Things: pithy wisdom summing up the core of any subject in two items. Some are honest attempts at encapsulating a topic:

The Two Things about Project Management:
1. The schedule will slip.
2. It's about how you manage the schedule slippage.

The Two Things about History:
1. Everything has earlier antecedents.
2. Sources lie, but they're all we have.

Some have a grain of truth but are mostly just funny:

The Two Things about Binary Systems:
One: 0
Two: 1

The Two Things about Web programming (as it is mostly done in the real world):
1) Control-C
2) Control-V

His original blog post on the topic includes more Two Things in the comments. And the emphasis on Two reminds me of this old joke.