You have to explain what you have forgotten you've learned to those without that experience
This applies when building software (especially web apps) and also to real life!
From the spurious pundit: Picture Hanging.:
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The key thing here is that there's a lot of stuff, from the detailed technical level to the long-range business level, that you just have to know. Your junior guy can't puzzle it out in advance, no matter how smart he is. It's not about being smart; it's just accumulating facts. You may have been working with them for so long that you've forgotten there ever was a time when you didn't understand them. But you have to learn to spell things out in detail, and make sure your junior folks are comfortable asking questions.
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