With great difficulty and annoyance. Once when developing with the 8051 family (using a development board that included a debugger), the program worked perfect

With great difficulty and annoyance. Once when developing with the 8051 family (using a development board that included a debugger), the program worked perfectly on the dev board, but when I burned it onto EEPROM, a subtle timing issue with a peripheral caused the program to fail. Much frustration ensued; had to develop that section with a long winded code->compile->burn->test cycle. Then we found out the particular 8051 variant we were using had been discontinued :(