The ThunkFactor is a metric for judging the worth of a document, for example course notes. Since YouArentGonnaReadIt (or rather your students aren't), it's important that your notes make a satisfactory thunk when thrown on a desk so that the student is led to believe that there's value within them.

----
Hmmm, I wonder how many projects suffer from this with their documentation?

-----
This brings us to the observation that, for a number of subjects, usefulness is inversely proportional to page count.
----
Mentioned with respect to course handouts on YouArentGonnaReadIt.
----
''Oh. So this has nothing to do with how much you thunk when you made the document. Hmmm.''

It takes an immense amount of thinking to produce a thin document.  Thick documents are thick because nobody thunk.  Which is why they go thunk when you plunk 'em.

----
See also: ShortBooks, TheAlmightyThud