Well, it really requires: A) great commit messages, B) comments that are worse than the commit message so that you have to go scavenge in revision control, C)

Well, it really requires: A) great commit messages, B) comments that are worse than the commit message so that you have to go scavenge in revision control, C) a single or very few commits where the craziness happened, and D) a codebase that hasn't drifted enough that this signal is hard to find. I've had poor luck spelunking for reasons in things like the Linux kernel. 90% of my revision control effort looks at things from the past couple of years, and before then it rapidly becomes diminishing returns.