Not sure if you’re wondering about general success (goals met) of weight loss, 1RM max, competition in running or lifting? Bodybuilding?
The above illustrates how all of us can benefit from having a mentor and coach regardless of level of experience. Most importantly, it keeps people honest with themselves and accountable. That said: training body systems can be very complex. The biggest mistake people make without a trainer is doing too much, too little, or inappropriate exercises, that won’t help them accomplish their personal goals.
The person who approaches exercise with tenacity, great skill set, and adherence to programming (with a coach) is usually the winner in life.