taciturn

taciturn \TAS-uh-turn\ , adjective:
Habitually silent; not inclined to talk.

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If I had been a bit more taciturn at times, it would've kept me out of a lot of trouble.

For example, if I hadn't said "I do."

Or, if I hadn't said "I'll do it!"

OR, if I hadn't said "I did it."