There is a purpose and a meaning behind each thing you ask the horse to do.
I see many people get on their horses and they let the horse wonder around and take over, then when the rider askes the horse to do something he takes you for a ride. You have to have a meaning and a purpose when riding. It dosent mean that you have to have a tough ride, it just means to look where you want to go and direct the horses feet there.
The horse learns not to be particular if the rider is not particular.
This is very similer with what I said above, if you let the horse go where ever he wants, first you are not being particular on where you want to go and second the horse will learn to zone out and not be particular on how he walks, moves and he will be less willing to work with you. So go where you want to go, ride the speed you want to go and be particular, even when you take a break.