<Theory X> is a post hoc explanation for how <Subject Y> works. It's not like somebody came up with the theory of how <Subject Y> should work and then built one, like you would a computer.

General relativity is a post hoc explanation for how large-scale spacetime works. It's not like somebody came up with the theory of how the universe should work and then built one, like you would a computer.

Darwinian evolution is a post hoc explanation for how life forms change over time. It's not like somebody came up with the theory of how life on earth should work and then built one, like you would a computer.