His model looks like this:
His big point is that disruptive innovation often starts out as a loser in the market. It overtakes what he calls "sustaining innovations" which are subsumed by the attractiveness of the disruptive alternative after some adoption time.
His video, explaining all this, is 8 minutes, and well worth the look.
Of course, Christensen has a lot more to say on this subject. For example, he posits five skills for discovering innovation:
While many business leaders tend to focus on honing their delivery skills, entrepreneurs and innovators must instead build the courage to start taking risks and cultivating their talent for discovery
And in his book, "The Innovator's DNA", he develops these five ideas for successful innovation:
(1) Associating: drawing connections between questions, problems, or ideas from unrelated fields,
(2) Questioning: posing queries that challenge common wisdom,
(3) Observing: scrutinizing the behavior of customers, suppliers, and competitors to identify new ways of doing things,
(4) Experimenting: constructing interactive experiences and provoking unorthodox responses to see what insights emerge, and
(5) Networking: meeting people with different ideas and perspectives