Ihave heard some talk lately about how technology will disaggregate higher education. The vision is that the likes of Khan Academy and Coursera will allow students to pick and choose courses and learning experiences to construct their own higher education — thus, it is asked, “Why do we need colleges, universities and dedicated faculties?” The Valhalla of limitless choice and student-driven learning presages an education built “piece-wise”: A little of this and a little of that pulled from a vast smorgasbord of providers at little or no cost to the student. What could possibly be wrong with that?

At issue here is the value of structure and system in higher education. A great education has a comprehensive vision about what an educated person should be or be able to do. At the heart of this comprehensive vision should be a commitment to systematic learning: One should know a little about a lot (breadth) and in one or more areas, should know a lot about a little (depth).

A piece-wise education doesn’t prepare you for life, and especially for professional life. You don’t stay long enough in one field to gain some deep insights. And you don’t gain the systematic breadth to help you connect dots across different disciplines. The partner in charge of recruiting for a leading management consulting firm once told me that he finds liberally trained graduates “so much more interesting” — able to express themselves well, talk on many subjects, be more creative, more self-confident in uncertain contexts, and so on. But there is more …

A piece-wise education can be less than the sum of its parts. There is a very strong synergy among fields and subjects. An understanding of economics benefits from knowledge of math. An understanding of politics benefits from knowledge of economics. Finance benefits from accounting. And so on. But this can work in reverse, too: Piece-wise learning might generate misunderstanding of related fields and a tendency to generalize from a very narrow knowledge base. As the saying goes, to a small child with a hammer, everything looks like a nail. Do we want medical doctors who know everything about pharmacology and nothing of surgery? Do we want bankers who know all about financial engineering, but not about ethics? Solutions to problems come from what you know. To the piece-wise educated, solutions to problems can seem deceptively simple.

You don’t know what you don’t know. A great education should cast daylight sufficiently far to instill respect for the sheer immensity of knowledge and of the pell-mell pace with which it is expanding. With piece-wise learning, you will see as far as your personal horizon, with no ken of what lies beyond.

You must own it; they won’t. The bland assurances of any provider — be it a college, nonprofit university, a for-profit or free online service — won’t protect you against getting a piece-wise education. You must want the systematic breadth and depth in order to get it. The failure of some schools to provide a more systematic education is saddening and inconsistent with their mission to society. Some schools underinvest in advising, tutoring, mentoring and career counseling. In those settings, you’re faced with a choice: Chart your own systematic breadth and depth, or risk piece-wise confusion, frustration and ultimate exit. The 64 percent dropout rate at for-profit universities is quite high and dwarfed only by the 90 percent dropout rate for Massive Open Online Courses.

Too much dessert and not enough broccoli. Students who simply follow their appetites will eventually find some educational candy: courses that may gratify an immediate interest, but don’t really build one’s capabilities. Like a healthy diet, a great education consists of a balance of intellectual nutrition. Eat your vegetables. They are good for you. Trust me.

Or, trust Johnny Cash. His song, “One Piece At A Time,” tells the story of a worker on a Cadillac assembly line who yearns to own one of those cars. So, he swipes parts over the course of 20 years, to the point where he is able to put together his own Caddy. Because the models kept changing year-to-year, the resulting car was a mish-mash:

Now, up to now my plan went all right

’Til we tried to put it all together one night

And that’s when we noticed that something was definitely wrong …

The back end looked kinda funny, too

But we put it together and when we got through

Well, that’s when we noticed that we only had one tail-fin

About that time my wife walked out

And I could see in her eyes that she had her doubts

But she opened the door and said “Honey, take me for a spin.”

So we drove up town just to get the tags

And I headed her right on down main drag

I could hear everybody laughin’ for blocks around

Johnny Cash’s song is a cautionary tale for piece-wise learners. It reminds us why structure matters: It promotes breadth, depth, and consistency of the pieces of learning that will form a whole greater than the sum of the parts.

Robert F. Bruner is dean of the University of Virginia’s Darden School of Business. This column was adapted from his blog.