If memory serves, the Mohawk people are all born with a total absence of vertigo, making skyscraper construction an ideal career choice for them.
If you think about it, what he is doing is simple, if you remove the inbuilt terror of falling that is built into our psyche so deeply, that we even feel uncomfortable watching him do what he does, knowing that he came to no harm, because the film is available.
With no fear of falling, he can walk a beam like walking down the street.