Why not? Human mind has its limits. The complexity of physics is orders of magnitude smaller than biology, let alone any kind of social science. Physics is the exception, not the rule. The rest of sciences are way more messy.
Almost anything outside physics is not predictable. Anything that involves human behavior is totally not understood, especially if it involves a bunch of humans (economy, sociology...). You could describe it, sure, but that is not the same as understating and modifying at will.
