The key is the word "meaningful". I know a lot of people (and I used to be one), who would shift from job to job and leave when things weren't right any more. But this typically seems to involve taking what you are as a person as given, preferring instead to simply try and change one's circumstances to match that.
It's much easier to find meaning in your work if you're prepared to allow what you are as a person be up for negotiation somewhat, in addition to wanting to exercise a degree of control over your working circumstances.
A reflection of this is pretty easy to see in the way some people frame their decision-making when deciding whether to get a new job or not. They ask themselves "is this really what I'll want?", as opposed to "is this what the person I'll be after a few years of this will want?" or "will this turn me into a person I want?". By unconsciously taking one's self-image as fixed in that way, it becomes harder to find meaning in work and as a bonus also makes it somewhat more likely that you'll make the wrong decision because your potential future mental state isn't accounted for.
Not saying you do this at all, but that there are a lot of shades of grey between being an intern and having to do what your bosses say slavishly. And a lot of them are only really visible when you look inward at yourself rather than outward at your environment.
I've got a job at the moment that's great because of this - it's not perfect, but being able to work on what I am at the same time as shaping what this job is makes the job of finding a happy means of existence drastically easier.