One can't proceed from the informal to the formal by formal means.
Some programming languages manage to absorb change, but withstand progress.
In computing, the mean time to failure keeps getting shorter.
To understand a program, you must become both the machine and the program.
If a listener nods his head when you're explaining your program, wake him up.
When a professor insists computer science is X but not Y, have compassion for his graduate students.