I was a system engineer on Pr1mos when I was a baby
Ah, I was a sysadmin on a few very big primos systems when I was a baby -- I wrote system tools, cool APIs and so on.
One day, I was making a new tool tool that was using shared memory; on pr1mos, there wasn't ANY ACL on shared memory, so you had to be a bit careful about what you were doing, thus ME, the trusted wizard, making APIs for it.
Anyway, my test program was taking a very very long time to start for a bizarre reason, and and I control-C'ed it, the phone started ringing with people on the same system complaining their their application was crashing and it seems the whole shared memory segment (for everyone) had been erased...
Of course, being the all wize admin, I blamed a glitch in the OS and/or a bug somewhere else and/or a cosmic ray..
But on that day, I learned to use parenthesis on *every* *single* *macro* and every *single* expression in my header files, and I've never stopped doing it.