Fried Egg in Cast Iron Skillet

I haven't had much luck frying eggs in any cast iron skillets in the past. I mean ANY. The eggs always stick like glue. I look around and find YouTube videos as demos. My mistakes have been the heat. I've been using medium-high to get the heat going faster. The heat needs to be medium-low. The cook oil needs to be enough to the cooking surface. The egg can be added. This procedure takes a long time and does work, but worth the time.