Here's a really simple question: How many characters have you played and deleted?
Let's exclude victims of restartitis, and focus on those characters you created, enjoyed and made some decent progess on (or even finished) and deleted. Why did you ultimately hit the button? Was it strange, erasing that time investment?
I don't remember them. However I accidentally sent one of my friend's characters into Oblivion. I saved over his epic file where he never died since leaving Helgen. It was one of the coolest quest I've ever seen. He made it to Windhelm by taking one of the longest paths, and most dangerous. He made it to lvl 17 with just the gear you get in Helgen's Keep. Deep down inside I know he doesn't forgive me for it. His name was Rohan Shiro, a Stormcloak recruit. The son of Mathyas Shiro.
I regret doing that. I wish to see how his playthrough would have went. My character was hardly worth of remembrance however. He was probably my biggest failure.
I have over 500 saves on my Skyrim, and over 600 on Oblivion. I've only ever deleted two characters. My first one, Simon the Imperial, because I got confused with Oblivion, was the victim of a deletion, along with a female dunmer pirate I made for fun, whose name escapes me. Aside from that, they're all saved on my hard drive, except for on Skyrim where my wood elf, Sirius, my Nord Olaf and my Khajiit Jak were deleted by my brother in a fit of rage.