Use yourself as an example to understand the remarkable capacity of human beings to walk great distances throughout their lives.

Fermi problems require you to make a quick estimate of a quantity
that seems difficult or impossible to determine precisely. They
were named after Enrico Fermi, the Italian physicist who used this
problem solving method to predict how atoms would work long
before scientists had the technology to actually see them. Fermi
problems emphasize the process of solving problems over getting
the exact answer.