They don't have to be yours. My mother's best friend got a new car. But she was having a problem with it; the engine was surging with a huge "ka-chunk ka-chunk" motion. She spilled her coffee on herself three days in a row on her way to work. So, she takes it into the shop. Mechanic checks under the hood, reports all systems go. Takes it for a spin with her in the passenger seat, everything's fine. Now she takes it for a spin with him. Immediately, the mechanic says: "Ma'am, please remove your left foot from the brake."