one thing leads to another idiom
一环扣一环；一来二去；自然而然
If one thing leads to another, there is a series of events in which each event was caused by the previous one.
At first, we were just talking a little, but one thing led to another, and he asked me out. 起初我们只是一起说说话，一来二去，他就约我出去了。