How the heck did people in the olden' days learn to beat eggs and other laborious tasks?
Accident and/or trial and error, with a bit of 'evolution'. Someone notices that cream gets a bit thicker when it's been stirred a while, they put two and two together and beat it. Then someone has the bright idea to use a whisk to get more air into it and make it even thicker, etc etc.

Though actually I imagine that whipped cream was actually discovered during the process of making butter (keep whipping cream and butter is what you get).