"Rome was not built in one day" says that we should not expect to build something great ("Rome") in a short period of time ("one day"). Example: "Are you still working on that same painting?" Answer: "Hey! Rome was not built in one day!" You must work hard and overcome many challenges if you want to complete your goal. Example: "It will be at least six more years of study before I can become a doctor." Answer: "Rome was not built in one day." The city of Rome, like all great works, was built over many years of hard work. "Rome was not built in one day" says that you must work hard and keep working hard if you want to build something great. Example: "It is taking me a long time to write this computer program." Answer: "Rome was not built in one day."