My last apartment oven ran 75 degrees hot on the bottom rack. I burned three trays of cookies to absolute charcoal before I figured it out. Just kept thinking I was suddenly terrible at baking.
Oh man, I was totally convinced my baking skills had just vanished overnight! I blamed my recipe, the flour, everything BUT the oven. Getting a simple oven thermometer was a total game changer, it completely fixed my problem. I felt so silly for not checking that first. Now I tell everyone to test their oven temp, it makes such a huge difference. You don't realize how off they can be until you see the real number.