How a Construction Crane is Erected (Video)

Well, there's no reason it has to be that way, except money and time. One could, in theory, assemble the base and initial structure by carrying individual steel rods and buckets of concrete to the site and assembling them all.

But the astute (and, perhaps, perverse) observer would note that this only pushes the problem farther down the stack. Using humans to carry your parts to assemble the base isn't really bootstrapping, either, because where did the steel and concrete come from? For that matter, where did the humans come from?

Unfortunately, we don't yet know how to depict humans being bootstrapped from raw organic chemicals at this level of detail, and even if we did it would probably run a bit longer than 6:17.