Why were the 1st 100 days so important for a president?

The idea of a presidents first 100 days wasn't really important until fdr took office. in his first 100 days he wanted to combat the great depression. he focused on creating jobs,getting the banks back on their feet, helping the elderly and poor, and revitalizing industry and agriculture (his new deal). to this day no president has done as much in their first 100 days as fdr did. he set standard for everyone and it's important because those 100 days are considered a way of "measuring" how successful a president will be.