The best thing to do is teach them to dig into problems, learn on their own, and think for themselves. They will have to learn how to deal with missing document

The best thing to do is teach them to dig into problems, learn on their own, and think for themselves. They will have to learn how to deal with missing documentation and unclear/messy code. They will have to learn how to unblock themselves when they are blocked, rather than just getting stuck. They will have to learn how to work around obstacles and think outside the box whenever the immediate initial solution that comes to mind turns out to not be a working one. Coworkers shouldn't be treated as StackOverflow unless absolutely last resort because it is incredibly distracting to answer mentees' easily-Googled questions about built-in language API calls every 15 minutes or so. A lot of programming is just professional Googling. Once they can function independently, they are no longer junior developers IMO, but this is a learned skill. When I started programming, I had enough people on IRC berating and insulting me for asking about standard C library calls that I learned how to research and solve my own problems the hard way (the acronym "RTFM" is toxic). It felt awful, and I can imagine a lot of people getting discouraged and just giving up. I was in high school trying to write my own malloc just for fun, and random strangers on the Internet kept calling me an "idiot" because I was still learning pointer arithmetic and needed help (and nobody IRL could help me).