Writing takes research! Does Rick Riordan know mythology so well that he just pulls that stuff out of his brain on the spot? Of course not! Funny example; he lists no sources or acknowledgments, not even on his website! BAD WRITER.
Good writers don't know everything.
Does your character have OCD? Do you know EVERYTHING about OCD?
Toten, Teresa. The Unlikely Hero of Room 13B. New York: Delacorte, 2015.
Does your character get arrested? Ever been arrested to know what actually happens in booking and jail?
Flynn, Gillian. Gone Girl: A Novel. New York: Crown, 2012.
Does your character drown in oil? What's that feel like?!?
Bacigalupi, Paolo. Ship Breaker. New York: Little, Brown, 2010.
Do know how an FBI profiler works?
Barnes, Jennifer Lynn. The Naturals. New York: Hyperion, 2013.
Septys, Ruta. Salt to the Sea. New York: Philomel Books, 2016.