I rode to the Oregon Zoo the other day and there is one .2 mile VERY steep hill that I go up and as I was at the mid point, huffing and puffing (as well as smiling) a female pedestrian said, "Keep going. You can do it!" and that made me feel great! I replied "Thanks" and it made me feel like I could continue on.
I guess hills are partly mental and partly physical. I think they require practice.