The phrase "really miss" is usually directed at something that one used to have/feel, but no longer do. So that is throwing me a bit, I think you are asking what concepts that you don't currently understand that would have made you a better programmer.

I don't think there is a good answer to your question, it could be nearly an infinite list. Being a Saint, I assume you have a lot of good understanding about a lot of things, so I can't shake the feeling that you've got a relatively short list of things already in mind, but chose not to share with us.

Need, and driving curiosity are the biggest reasons most people will learn new things. So, if you have a need, or can see how something might make life easier for you in the relatively near future, the barriers to new comprehension tend to be pretty low. Or a driving curiosity for whatever reason can help in learning new ideas/skills.

So, yes, I think all of us feel some desire to learn something that we don't currently have the time/energy available to pursue. The next step to further enlightement? The next new need that shows up in your life; whether that's an actual need or a driving curiosity doesn't matter for the end result.

But, you need to have some knowledge about what else is out there, and how it might apply so you know that this IS an opportunity to learn something new. So, I choose to read a lot of posts here at the monestary. Browsing CPAN can help. Staying knowledgable about other languages, industries, etc. It all involves a lot of reading, or listening. I guess it really boils down to: stay involved; don't get complacent.

-Scott