Usually it's small things I find annoying, when just looking at the code it with fresh eyes is enough to unveil small idiocies. It's easy to judge because I don't need to sugar coat any criticism I have when I'm the one under the lens. This stuff is usually the result of refactoring too quickly, and not rounding off all the corners, especially if the code I was refactoring was new code.
More embarrassing is when I find flaws in my assumptions or thought process: things that are more complicated than they should be, or inability to separate an idea from the engineering context it emerged from. This is usually the result of rushing through something (often towards the end of a project) and not thinking things through, being ignorant of a better approach, or just plain old lack of insight.
This process used to make me feel bad, but now it makes me feel good. I used to be concerned with how fast I learned things, eager to understand ideas that would propel me towards finding the ultimate paradigm [singular. ugh!] of the future.
When your goals are as laughable as that failure makes you feel bad.
I think now I'm much more relaxed about everything. I'm not looking for a silver bullet at all anymore. I'm looking for fun ideas to "spice up my routine" as they say. If I remain interested I usually produce dramatically better results than if I need to force myself to work.
Leisure has replaced ambition as the primary purpose of my learning efforts.
However, without ambition to drive me forward, I occasionally feel like I'm not trying hard enough to better myself. Seeing past failures (especially recent ones) is an great way of reassuring myself that my brain has not in fact crawled under a cupboard and died.
Recognition of past failure was always evidence that I am still learning, but in the past I thought it meant that I was not yet any good. Now it just means that I'm still having enough fun to stay curious, and I'm also learning what I should be unlearning.
So now that I am old and wise, I know that when I grow up I want to still be having fun, or at least to realize why this blog post is full of shit.
 Unfortunately the backpan directory listing doesn't seem to have the dates right, so the linked listing doesn't contain mistakes that have been superseded with new module uploads, only ones big enough to completely give up on, or that have been fixed by other people ;-)