I worked at my previous job about 8 years (hired out of school) and wasn't actively looking for a new one; I had a lot of freedom and liked my boss and colleagues, but the pay was mediocre and I was under a lot of pressure because I was the sole architect, engineer, and programmer for a good number of important applications.

Anyway, my brother-in-law told me that his employer was looking for a developer and that previous candidates fell through, and that the pay was a lot more and they're good about raises (which was like pulling teeth at my then-current job) so I applied and went for an interview.

They basically gave me an offer on the spot and wanted me to start in 2 weeks. I told them that it would be hard since I'd basically be cutting my boss's Achilles by leaving so soon and suddenly (just hiring someone would take at least a month, not counting getting applicants), but they were adamant, as the position had been vacant for a few months at that point. I got them to agree to 3 weeks and pulled the trigger, but offered to help out in my old position for a few months cause we had a big project in progress I was leading.

So the new job is great: it's a much younger office and I'm having more fun and there's a lot less pressure. Meanwhile, at the old job, the project I was leading got scrapped and the asked me to do other odds and ends until, after screwing something up I basically told them I'm done. They got a new guy quickly due to a lucky turn of events, but he couldn't pick up where I left off on a lot of projects: they're going to rewrite one because of it. My one colleague still likes to point out that I left without them having knowledge of my code (besides that I always said I'd answer questions, plus it's been 6 months now and my code is all on a TFS instance they all have access to).

I still feel a bit guilty even though I have no reason to.