気になる vs 気にする — which one is 'I' doing the worrying vs the thing 'making' me worry?

Question

彼のことが気になる vs 彼のことを気にする. Both translate loosely to 'worry about him' in English but I think the grammar direction is opposite. Can someone confirm?

Accepted Answer

Confirmed, and this trips up a lot of learners. 気になる is intransitive — 'something (marked with が) becomes a thing weighing on my mind', a bit more passive/spontaneous (you can't fully help it). 気にする is transitive/volitional — 'I actively worry about/mind X (marked with を)', closer to a deliberate act or reaction. 気にしないで (don't worry about it / don't let it bother you) uses the volitional one because you're asking someone to actively let go of a reaction.