They are ordered by increasing contact with reality - no elegant plan survives that. The constraints of available resources and the details of what it is actual

They are ordered by increasing contact with reality - no elegant plan survives that. The constraints of available resources and the details of what it is actually for take their toll. Elegance requires constraints consistent and few, whereas reality is a seething mess of capricious special cases - the far end of the spectrum from pure consistent abstractions. But not only that it's easier, he also means that a solipsist chasing idealized butterflies is not an engineer. An engineer is meant to solve real, practical problems.