Why does hardware break down at 2 AM?

Yesterday, right when I was about to go to bed, I suddenly noticed that rock, my workstation, wasn't acting normally anymore. Since it runs spamd for my mailserver (which I would prefer not to implode on mail), I investigated immediately. Apparently, the network card had broken down.

sigh. And I had to go to work today, which didn't happen as planned

Actually,

Why does hardware break down at all? The only replacement network card I had left was a 3Com EtherlinkII. So, ISA. Not exactly state of the art...