No it's fine.
We all try and put together the best roster and set up gameplans with rules to give ourself every possible advantage in a game but.....
Luck is a factor
From my understanding, every play is a series of dice rolls based on all the variables that factor into the equation.
Take your avoid fumble scenario. A 90 avoid fumble RB coughs it up 3 times in a game.....maybe he is tackled by a 90 force fumble MLB which creates an ???? 80% chance he fumbles....still good odds but the sim rolls over 80 all three times.....bad luck.
Dont get me wrong, I dont think I'm unbeatable or only having bad luck will cause me to lose. I beat Oakland/Crazyrazor by 3 in the regular season so going in I thought it was 50/50.