CM, While I'm not a real engineer I did get a degree in said topic. One of the things that struck me then and now is that a lot of engineering is based on rules of thumb derived from empirical data. The public tends to think of engineering in the computer age as knowing and accurately modeling things based on physics alone when there is still a large part played by rules of thumb.
One example: on a tail rotor helo, it works better if the forward blade is traveling up, I've heard all sorts of theories as to why and yet Ray Prouty wrote once that know one really knows why. It's enough to know that this setup works better, so there's no reason to delve into it further and another rule of thumb is born.