If you've ever started doing something only to realize your plan wouldn't work out and you had to start again, you've gone back to the drawing board.
The drawing board in this phrase refers to a piece of equipment used in technical drawing. It's an angled surface, often on a stand, designed to hold paper and drafting tools for precise sketching. Engineers and architects use it when designing prototypes or buildings. The phrase go back to the drawing board became popular due to a famous cartoon by Peter Arno, published in The New Yorker in 1941. The cartoon shows an airplane crashing in the background while a man holding blueprints walks away, saying, "Well, back to the drawing board."