As I said previously, we don't have any hills here but I was doing a club ride a few years ago in an area that had hills...I gutted my way up this long steep grade and chanted to myself "don't you DARE quit" all the way up. I reached the top and felt utterly spent...then a rotweiler launched himself off the top step of a nearby farmhouse and gave chase...it was amazing what reserves I had left when I felt "spent".