I don’t think it’s mental gymnastics I think it’s a lack of actual gymnastics, so to speak. Body odor mostly comes from sweating so if you don’t sweat much you don’t need deodorant near as much. Someone with a healthy body weight living a largely sedentary lifestyle in a cooler climate might not need it at all and might smell perfectly fine with showers every other day or even every third day. However, that’s best case scenario and most people don’t check all those boxes. If you’re overweight, move around a lot, or just live in a warmer climate then that’s not going to work.