Also learning to explain how and why one feature is stupidly simple and another is exceedingly impossible has been an interesting challenge.
Otherwise nothing particularly revelatory, you will hear all of the typical “learning the people skills” stuff from me. Also people complain privately to their managers way more than you would think.
Essentially, the first draft of a product that does what it needs to do to show capabilities to others. Similar to a proof of principle
EDIT: Thanks for the clarification @kweinber, an MVP is put into production whereas a PoC/PoP is not
xkcd  made an ingenious comic about this that I keep coming back to