Have you ever ridden a unicycle?  It takes great balance to ride it since there is only one wheel that touches the ground.
I have not. I do not have good balance even when walking so I can't imagine trying to ride a unicycle!
I understand.  I think the unicycle is great.  In fact, they have recently started to be used to create different sports like unicycle hockey!  
That sounds really interesting! It would be fun to watch people trying to play sports on unicycles!
Yes.  The unicycle hockey is just like roller hockey, but, obviously, the players have to ride on unicycles.  
Hockey in general is hard to play. I can only imagine while trying to maintain balance!
Think about this: in recent years, unicycles have also been used in activities like mountain biking.  Again, mountain biking itself is difficult enough on a bicycle - now try it on one wheel.  Amazing.  I could never do that.