Hills humble runners.
Even a mole hill is sufficient to tire a marathoner down in a merely a kilometer. Gradients are always harder than they appear, especially when one runs uphill. Besides, the losses are asymmetric. The downhill would probably add only a fraction of the pace that the uphill takes away.
Nevertheless, runners love hills. They serve as ideal training grounds. Practicing on a steep hill is the quickest means to develop the right muscles.
Whenever conditions are less than ideal to perform at one’s best, there is an opportunity to train hard. After all, the quality of our training sets the tone for our performance on race day.