There's always one more bug.
Any program will expand to fill 100.5% of all available memory and disk space.
Just because you wrote it out doesn't guarantee you can read it in.
Any interface that is stable and well-documented is already obsolete.
There is no such thing as a "standard configuration".
Never test for an error condition you don't know how to handle.
"Undocumented" is short for "isn't tested and doesn't always work".
Antique software will be run on state-of-the-art hardware, and vice versa.
Source code is not documentation.
Never underestimate the user's ability to ignore the obvious.