There are a number of factors - and you are accurate in thinking those are effecting the play. The field of vision skill will help the QB identify defending players and also locate an alternate open receiver, so it improves his decision making when he throws the ball. The look off defender skill basically is his ability to move the safety (or other zone coverage db's) out of position by looking at the non-primary receiver, although that competes against the db's zone coverage skill (and does nothing if there are no db's in zone coverage). If the QB is under pressure, his accuracy will suffer. And on the defensive side, if the db's have good man-to-man skills vs. your receiver's route running skills they are going to have good effective tight coverage. And lastly there is just the dumb luck dice roll that could turn the perfect situation into a bad one, and sometimes it does seem that you get all the bad dice rolls in a game.
The coaching is probably the least influential, the coaches are impacting the player development more than they are their game performance.