to start doing something, often without intending to

We've fallen into the habit of getting up late on Saturday mornings. 我们开始习惯周六早晨睡懒觉。

I fell into my job quite by accident. 我从事这份工作很大程度上是出于偶然。

She fell into a conversation with the taxi driver. 她和出租车司机交谈起来。

to gradually get into a particular condition, especially to get into a bad condition as a result of not being taken care of

Over the years the house had fallen into disrepair. 过了这么多年这幢房子已破败不堪。

The old school fell into disuse (= people stopped using it). 老校舍废弃不用了。