[philrea]

Write a relatively complex system without any external code and, preferably, without any previous training...

It will suck, it will break, and eventually, it will be near impossible to add or change anything at all. But you will have experienced what the patterns n' principles authors (better) have and, I bet, even "accidentally" used a few of them.

In my opinion, design principle = minimize dependency. Oh and, if you do follow my suggestion, use a language that isn't object oriented... at the least you will, like me, wonder why "object-oriented something" isn't explicitly defined by gof elsewhere and, at better, might "accidentally" implement some sort of custom object system

I am gonna go ahead and say it... REINVENTING THE WHEEL IS A GOOD AND NECESSARY THING... if done for the right reasons, in the right circumstances...