Two days into Apollo 13's lunar mission an oxygen tank exploded, crippling the command module. Mission Control had to bring the crew home alive using only what was already aboard the spacecraft — including improvising a CO2 scrubber from a sock, a cardboard manual cover, and duct tape. The mission failed; the crew came home.
The principle: Sometimes the constraint that defines the solution is what you have right now. The right move is not 'what would solve this' but 'what would solve this using only the components in the room'. Constraint is a creative input, not just a limit.