You know if you did your best - and got the most out of your material. Must be fun for players. Wince on every mistake. Players lose confidence - complain only on effort. They must be able to think on their feet.
Success is a lot mental - have confidence once mechanics mastered.
Everyone hears your every word. Must develop bench, hopefully 2 deep at every position. If you have even talent, then you can sub more - play until you give up 2 first downs, etc. Everyone can come out for a couple of plays. Gives subs great confidence to play in first.