if you happen to do something, you do it by chance 碰巧[凑巧]做某事
I happened to see James in town.
我碰巧在镇上遇见詹姆斯。
Examples from the Corpus
happen to do something• It happens to all of us.• These bands just happened to be black and popular.• I'm sorry I didn't phone first -- I just happened to be passing and thought I'd drop in.• Justin forgot the map but I happened to have another one in the glovecompartment.• We're not related -- we just happen to have the same name.• What will happen to her during the war?• I'd be arrested, Volkov wouldn't know what had happened to me.• She kneels down and gathers me to her, sobbing and shaking in her terror at what might have happened to me.• I happened to see Hannah at the storetoday.• What happens to the structure of a potato when it is cooked? 2.• Tell me first, what happened to the world when I was in prison.• They don't learn by experience, don't really care what happens to them.