Help me ask why you didn't just

Now you understand the problem a little better, and you understand the shortcomings or deficiencies of a pre-existing solution a little better, but you're signalling to the person you're asking that you're looking to second-guess their judgment or wisdom before you even understand the problem that was trying to be solved. Why didn't you wait until you understand the problem well enough such that you'd be able to see (along with them) why an off-the-shelf solution wouldn't work? Asking why a specific off-the-shelf solution wasn't chosen is a way of signalling to someone else "hey, I don't understand the problem very well but I'm sure that I have a better solution". So don't ask why a technology wasn't chosen; ask questions about the problem domain until you understand why - WITHOUT asking.

Here's the other scenario: you know for a fact that an off-the-shelf solution would've been a better choice than what someone else did. In that case - guess what? Don't ask: tell. Don't patronize someone by saying "why didn't work here in a case where it obviously was a smarter choice"; instead, have the courage to say "I think that a better use of time would've been doing research and seeing if was usable." Because if you're trying to tell someone that they made a mistake by reinventing the wheel, asking them why they reinvented the wheel rather than telling them they did so will probably be seen as patronizing or dishonest.

Either understand why the first thing that popped into your head doesn't work without having them tell you why that's the case, OR be so certain that the first thing that popped in your head does work that you're willing to declare that. Anything else is inviting people to believe that you're trying to "stump-the-chump", so to speak.

This is bad advice and I hope nobody takes it. We learn from each other. I've very glad I didn't have to learn everything I know first-hand.

Personally I am honored when people think highly enough of me to feel like they can learn from my experience. I also like learning new things, so if there was some obvious answer that I just missed of course I want to know about it!

The correct answer is first form a relationship, then ask. The author worries:

I have realized I honestly don't know how to express my question to make clear that I mean #2, without including a ridiculously long and pleading disclaimer before what should be a short question.

It's perfectly ok to have that long preface the first time you ask this kind of question. "Sorry to be long-winded, but since we don't know each other that well yet I just want to be clear: I don't understand why you didn't choose XYZ? I'm interested in learning about this but I haven't spent as much time on it as you have. I would have tried XYZ but I'm assuming there was some issue. What was the issue?"

In general over time people will learn your character and your intention. If you are truly humble and trying to learn they will come to expect that attitude of humility from you and the long preamble won't be necessary.

In situations where you don't have the opportunity to build a continuing relationship just accept that the verbosity of your question is the price of clear communication without the context of an existing relationship.

But please, please keep asking questions, even if they seem obvious. That's how we grow.

In most cases, showing curiosity and asking questions in code reviews goes beyond educating yourself: it's also about providing "self serve" context for future developers who need to understand why a specific decision was made.

This context can also, for example, prevent future developers from trying to refactor or rewrite entire pieces of a program to follow "what first comes to mind".

I'm curious to know about the kind of projects you work on and how you've seen the approach of asking fail there.