It's just a review tool designed for storing Question / Answer pairs to your long-term memory. Nothing else.
If that means using it to review and remember specific answers to WHY questions (Why is the sky blue?) for the rest of your life, all power to you. Keep reviewing. However, I think the moment you start asking these conceptual questions you're no longer just trying to remember - you're trying to understand. That's not what flash-cards are designed for.
Instead, you might actually want to look at the sky. Do experiments. Meet experts.
In the process, you will come up with new questions and new answers to old questions. More importantly, as a result of this adventure you will not only remember, but also learn. I wonder if Newton used flash-cards.
Yes, is is designed for storing QA pairs, but it doesn't mean it can't be used for anything else.
I believe you misunderstood the use I have in mind for the WHY questions. The idea is not to create cards for things you are trying to understand, but for things you already understood.
These things you describe are about learning. Flash cards/Spaced Repetition Systems come AFTER learning. Say, for example, you meet an expert and because of that have a great insight about issue X. Truly, real "insights" take longer to forget than rote memorized facts. But can you say you will remember this insight in 6 months if you don't serendipitously encounter it again? 1 year? 5 years?
That's where a reviewing system comes into place. And it's not because such a system is designed for things that mostly need to be rote memorized that you can't use the "question" as a trigger to revisit something of a different nature.
If that means using it to review and remember specific answers to WHY questions (Why is the sky blue?) for the rest of your life, all power to you. Keep reviewing. However, I think the moment you start asking these conceptual questions you're no longer just trying to remember - you're trying to understand. That's not what flash-cards are designed for.
Instead, you might actually want to look at the sky. Do experiments. Meet experts.
In the process, you will come up with new questions and new answers to old questions. More importantly, as a result of this adventure you will not only remember, but also learn. I wonder if Newton used flash-cards.