I prefer to think about these rules in terms of bets. Adding e.g. a symbolic constant is a bet. You win if during the lifetime of the system, you discover that

I prefer to think about these rules in terms of bets. Adding e.g. a symbolic constant is a bet. You win if during the lifetime of the system, you discover that the constant must be changed, and the gain is the time saved by changing it quickly and with few errors. If you never have to change the constant, you lose the time spent on introducing the constant and the time spent on looking up the constant while reading the code. Most of the rules here are long change (or whatever the financial people call betting on something), except for KISS.