If your story suffers from cardboard characters, it probably also suffers from plot contrivances. Good news: if you fix one, you fix both.
Ep. 594: 8 Ways to Avoid Cardboard Characters (and Plot Contrivances While You’re At It)
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If your story suffers from cardboard characters, it probably also suffers from plot contrivances. Good news: if you fix one, you fix both.