In a word: Context.
I distrust textbooks (they're outdated before they're published), and wikis don't fare much better. Primary literature and review literature are wonderful, but have their own drawbacks.
A brief word on each of these resources follows, then why I need an instructor to help me put it all together.
Textbooks are meant to give context, either for an entire field or for a subfield. Some textbooks age well, while others do not. For myself as a trainee, the problem is that I do not know exactly which parts have aged well, and which should be updated. When I pick up a textbook myself, I hope the parts I read will be both accurate and up-to-date, but digging through the new primary literature to verify every piece would be a herculean task.
UpToDate is a great wiki-style tool, with good tracing of provenance and upfront reporting of recency, and it comes in bite-sized chunks that are easy to use in a busy clinical context - but it also comes in bite-sized chunks, and in a busy clinical context clicking through the hyperlinked rabbit holes that would give me the rest of what I need to know is unlikely, and error-prone. Primary literature takes me right to the bottom of the rabbit hole, and as a physician-scientist, primary sources make me happy and comfortable - but it