I like to try to understand what someone is hoping to get out of their job. People have any number of reasons for working, from 'putting food on the table' to 'changing the world.' There are a lot of intermediate motivations as well.
I try to understand that because I have a fairly good idea what the job can offer and the extent to which the job can be tailored to help align it with the employee's goals.
I try not to generalize. I start with the thesis that someone who loves their job and that job is meeting all of their current personal goals, will stay working on it until one of those two things changes. In my experience that sort of change generally takes years not months.
When people go job to job to job, it can be simple like they are trying to ratchet their salary up faster than the typical 'annual' raise cycle. It can be complex like they are taking jobs that meet some requirement they have imposed on themselves but they don't actually like those sorts of jobs. Or it can be something else entirely. I'd like to understand what it is so that I can gauge whether or not the person is likely to stick around long enough to have an impact or not.