So if you follow any sort of online cookery page, you’ll see people recommending how to heat up a frying pan and add oil – which to do first and why. This is the definitive answer: heat up your pan to the approved temperature for a few minutes, then add the oil/butter/fat, then immediately add the ingredients you want to cook.
Why? If you add the oil at the start it will heat up at the same time as the pan and burn before the pan itself is up to the correct temperature all over. The bottom of the frying pan will heat up quickly, with the sides taking a while to heat up. You want the whole pan up to temperature to ensure even cooking of your ingredients. If part of it is still cool, it won’t sear your ingredients in the approved way. Instead, being cool, it will allow the water in the ingredients to boil and steam in place, cooking your ingredients at 100°C instead of 200°C+. They won’t look pretty, there will be no Maillard Reactions, and it won’t taste as good.