Option 1: lucrative -> means profitable/financially rewarding, but the sentence focuses on emotional and self-discovery benefits, not money.
Option 2: thriving -> means flourishing or prospering, which doesn't appropriately describe an activity's effect on the writer.
Option 3: restrictive -> means limiting or constraining, which contradicts the positive benefits mentioned (self-understanding and good feelings).
Option 4: therapeutic -> means healing or beneficial to mental/emotional well-being, which perfectly aligns with gaining self-understanding and positive feelings.
Hence, Option 4: therapeutic -> The word "therapeutic" perfectly captures the healing and mentally beneficial nature of writing poetry described in the sentence. The context clues "truer understanding of myself" and "good feeling inside" indicate emotional and psychological benefits, which is exactly what therapeutic means. -> correct