Well, on the other hand, if you know a bit about hardware, it is fairly easy to build a simple yet fully functional processor from basic components, implementin

Well, on the other hand, if you know a bit about hardware, it is fairly easy to build a simple yet fully functional processor from basic components, implementing an OS with most common features and a compiler with advanced error checking and an optimizer is also doable. You probably need to be familiar with math as well. Now anyone with this knowledge can become very expert in whatever field he is interested in. Why would you know everything, from electrons to software ?