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nature; disposition
私は内向的な性分なので、賑やかな場所は苦手だ。
I'm an introverted person by nature, so I'm not good with lively places.
凝り性な性分なので、何度もやり直す。
Because of my painstaking nature, I redo things many times.
心配性な性分は直らない。
My worrying disposition won't change.