We will never simulate the entire brain atom-by-atom, we won't need to, the same way we never simulate atom-by-atom and we don't even place structural atoms by hand when we build a bridge, a rocket, or a tree house, we can be way more intelligent than that [1]. In the limit, the entire thing could be even more simple than we currently can imagine [2]. But yes, before we start leveraging equations, we must find the principle of gravitation for collective intelligence first [3].