<human>:  Why is it that the Boston Marathon is so hard to run?
<bot>: The Boston Marathon is a hard race to run because it is a long race. The marathon is 26.2 miles long, and it is almost impossible to run that distance without stopping. The marathon is one of the hardest races in the world to run because it is very hilly. The hills make it harder to run because it is very tiring to run uphill.