It wasn't a good analogy. For one thing, toddlers don't tie their shoes: the average age for learning to tie your shoes is 6 years old. And it's not clear that kids will learn for themselves if you give them a few hours. We're not talking about letting junior engineers struggle for weeks or months, but they can bang their heads for a few hours or maybe even a few days and figure out a lot of things for themselves. That's a useful skill to acquire.

Here's my analogy: if you want to learn how to ride a bike, you've got to take off the training wheels, and sometimes that means falling over.

I don't think you get it. Letting a junior engineer bang their heads for a few days on something you could show them in ten minutes is just a waste of time and money. In my experience there are PLENTY of real problems for them to solve, things I DON'T know the answer for.

You can't just consider one question and one answer in isolation. The questions and answers add up. It's a waste of the senior engineer's time to spend ten minutes each answering every question of junior engineers who are constantly asking questions, seemingly incapable of helping themselves. The senior engineer becomes a glorified babysitter, and the junior engineers then never learn to solve problems for themselves, which will waste everyone's time in the future.

Not every problem is going to take junior engineers days to solve for themselves. I was stating an upper bound of how much rope to give them, not an average.

Besides, what happens when the senior engineer leaves the company? Sometimes "institutional knowledge" walks out of the institution.

Yes, what happens when the senior engineer leaves the company, having never shared his or her knowledge?

It sounds like you are trying to address issues during mentoring that should have been addressed during the hiring process. In my experience, all the juniors I've worked with come in with the idea that they can solve every single issue themselves, and part of my job is to show them how wasteful that is, that a simple question can save the whole team days if not weeks worth of time.

If someone walked through the door who is not enthusiastic about solving technical issues themselves...your hiring process needs work.