Most people who get overtraining symptoms are people who either train really stupidly and/or do not take recovery seriously. That means getting enough sleep, food, rest and recovery sessions, stress reduction etc. If you can not do these things don't go abd train like.someone who can. Work and family life is a stressor so you learn to deal with stress better to accommodate these things. Most athletes don't have these stresses and the good ones manage these stresses well (or learn too).
Food wise people seem to do either eat too much or eat too little. Sadly the average trainee goes towards the two little side of things and can not recover properly because of it.
You will always get a crazy trainee who maxes out his bench press 4 times a week and then overtrains but that is rare. In short most people under-recover not over-train.