This is good advice and I've actually followed it for estimating software projects. If you say 4x of what you think, and your boss/client doesn't balk, you probably have it right.
I'm roughly between 3x and 10x off, depending on the type of work. For greenfield work on small well-understood tasks and with application and test infrastructure setup, I'm ~3x off. Constantly changing complex applications without tests, I'm ~10x off. However even these multipliers have a 1-20x margin of error.