Collapse of the aerodynamically misdesigned Tacoma Narrows BridgeAP Wide World Photos
I beseech you, in the bowels of Christ, think it possible you may be mistaken.
OLIVER CROMWELL 
But when I make a mistake, it is a beaut!
FIORELLO LA GUARDIA
The besetting mistake of expert designers is not designing the thing wrong, but designing the wrong thing.
In any field, the amateur makes lots of little mistakes that a professional would never make. Training, internship, and practice have drilled the professional on good technique.
Professionals, when they goof, do it in a big way—making bridges that collapse ...