The first thing I learned is probably most important - full control of private keys is something that guarantees security, every user should become their own bank, so why so many trusted some online exchange at that time. Just because it was easy to open account there, and the possibility of hacking is not taken seriously.
I just check when first version of Electrum is released, and that was back in 2011 which was a surprise to me. Just two years after BTC appeared on the scene there is option for lightweight wallet, and to download whole blockchain also was not a problem. People always choose the easiest way, no matter how much this way is unsafe.