The Unexpected Virtue of Ignorance
It's the title of Tabitha Dickinson's review about the play. She's a critic, initially she detests Riggan and his play but after actually watching it, she turns in a positive review praising Riggan's performance and his play.
A similar question was asked here and there's an excellent answer by a user.
Tabitha Dickinson is a critic who is deeply ingrained in the history
of theater, specifically New York theater. To her, somebody who
hasn't spent time in the theater is an amateur. They should spend
time building up their skills and investing in the experience. She
doesn't consider movie and TV acting as the same skill. She's seen a
lot of theater that breaks the rules, and most of it has been very
The line refers to her being impressed with this show. Though he has
no experience, he has created a show that works well. An ignorant
person has made choices that an experienced Broadway director
wouldn't, but they worked.
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