Back in the late nineties I worked with a software called Origin. It had a BASIC like programming language where variable names consisted of single letters. If you now think 26 variable names should be enough: Some of the letters, like X and Y, had special predefined meaning and you couldn't change that. If you used seem you encountered strange behaviour, like values changing behind your back. To add insult to injury I could never find documentation about which variables were special, so I stuck with the few I new were safe, which were not many...