Full Idea
On the 'familiarity' model of explanation, unfamiliar phenomena call for explanation, and good explanations somehow make them familiar.
Gist of Idea
An explanation is what makes the unfamiliar familiar to us
Source
Peter Lipton (Inference to the Best Explanation (2nd) [2004], 02 'Reason')
Book Reference
Lipton,Peter: 'Inference to the Best Explanation (2nd ed)' [Routledge 2004], p.24
A Reaction
Lipton notes that his encourages explanation by analogy, but that may not add to understanding. A better version is that an explanation makes a phenomenon less surprising (but that sounds rather relative and subjective).