I have had good success determining the doneness of burgers but pressing lightly on them with my finger whlist they are cooking. It takes some experimentation to learn the levels of firmness and how it relates to doneness. I realize some folks will object to having their food touched in this manner, so I only do it when cooking for me and my family.
I second the use of a thermometer, when practical.
I used to be a racist, but I don't have much interest in it since Dale Earnhardt got killed.
Outside of a dog, a book is a man's best friend. Inside of a dog, it's too dark to read.
Good judgement comes from experience; experience comes from bad judgement.