Something wonderful.
Even the Panama Canal would never have been built _simply_ to let ships through.

It is the pure disinterested craving of the human male to make something wonderful, out of his own head and his own self, and his own soul's faith and delight, which starts everything going.

This is the prime motivity.

And the motivity of sex is subsidiary to this: often directly antagonistic.
That is, the essentially religious or creative motive is the first motive for all human activity.

The sexual motive comes second.