When you’re out to dinner with friends and they know you’re on a diet, your not going to splurge on that chocolate cake. Or if you do, you will feel the need to justify it. If you have a workout partner, you aren’t going to consecutively miss 3 or 4 workouts. Or if you do, you will feel guilty.
It’s definitely good to have people or checks in place so you stay true to your decisions.
Yet, try taking those away and see how you do. You might be surprised at how little self discipline you have. You might be shocked at how much you rely on other’s expectations of you to keep you consistent. I know I was.