I'm more willing to give my horse a 'chance' to behave well, because I know him better. School horses, I wouldn't ground tie and leave loose as I tack up and brush, wouldn't work without them tied in a stall with food, wouldn't trust so much with other people on them.

I think in my case (I'm just as demanding expecting my horse to have decent manners-if not moreso) it's more that I know him well enough that I'm willing to take the risk to give him the chance to be good.
Greater risk, greater reward-and because I know him well enough I can assess the risk more accurately and decide whether or not it's worth taking.

“There's a lot about discovering who you are and how difficult that is, and it never stops.”
- Libba Bray