The business model

Value created, value captured.

Two halves

Creating value means solving a problem someone has. Capturing value means being paid for it. Plenty of useful products fail the second half and disappear.

Ask who pays, how much, how often, and why they keep paying.
Free products capture value elsewhere: advertising, data or an upgrade path.

Unit economics

What a single sale earns after the costs directly tied to it. If that number is negative, growth accelerates the losses rather than fixing them.