I would go as some said about the interviewer would like to hear about your ACID knowledge but in a case where he would absolutely like something:

Running some concurrent queries with NOLOCK or READ UNCOMMITTED isolation level could break the ACID property. (The I one)

From wikipedia:

The isolation property ensures that the concurrent execution of transactions results in a system state that could have been obtained if transactions are executed serially, i.e. one after the other.

Because of page split you might obtain a different result than having those requests done sequentially.

I'm sure there's other answers also but this one that came up my mind.