In a Rails "shop" software company, it is most likely that developers and their leads do not know all the libraries (called gems in the Ruby world) their applications use. You should not be surprised when you pick a random gem from their Gemfile, ask a software engineer who has worked for 3 years in that company what that gem is used for, and you get the answer, "I don't know."
I thought, I myself should not be in that precarious situation. I should know all the gems that my projects used.