Clayton Christensen called it “disruptive innovation.” Lester Thurow called it “punctuated equilibrium.” Thomas Kuhn called it a “paradigm shift.” Whatever you call it, you know it when you see it: Worlds turned upside down by fundamentally new innovations that render yesterday’s truths suddenly false.

These events tend to favor new entrants at the expense of incumbents who are often found clinging in vain to the precepts of faltering beliefs. Others get on board by dint of courage, wisdom or—perhaps most often—the pragmatic view that martyrdom and willful ignorance rarely end well.

This pattern is playing out today in the world of enterprise IT, where a bookseller has turned traditional notions of IT utterly on its ear. (Oh, one more truth about these disruptions: They tend to sneak up on you from unexpected quarters!)

Public cloud services such as Amazon EC2 have fundamentally changed the performance and economic expectations of modern IT organizations. IT used to be your cable company: Slow, bureaucratic, often inefficient and not terribly service-minded. That’s because business lines had no choice but to wait.

At the same time, IT operating budgets that were once expected grow are doing just the opposite: IT is now expected to do more with less.

Along comes Amazon and it’s “16 digits to freedom,” according to Rodrigo Flores, CTO of newScale. It’s the swipe of the credit card and the release valve for pent-up demand that allow applications and workloads to escape to the cloud.

It’s hard to overstate what this all means for enterprise IT. The question echoes through the hallways of most any data center today: “Amazon can do it. Why can’t you?”

It’s the essence of this question that’s forcing a transformation in IT delivery models. This transformation will approximate four progressive phases: