Just as Princess Elizabeth - later Queen Elizabeth II - was a vehicle driver/mechanic in the ATS, doing her part for the war effort in WWII, I guess younger Celestia learned the value of hard work & responsibility.
Thus her becoming the wise monarch of Equestria, many moons later.
Thus her becoming the wise monarch of Equestria, many moons later.
Source of the source: http://silfoe.deviantart.com/art/Ascension-Page-1-540044132