  I draw attention to the fact that three recently proposed physical
principles, namely "local orthogonality", "global exclusive disjunction", and
"compatible orthogonality" are not new principles, but different versions of a
principle that Ernst Specker noticed long ago. I include a video of Specker
stating this principle in 2009 in the following terms: "Do you know what,
according to me, is the fundamental theorem of quantum mechanics? (...) That
is, if you have several questions and you can answer any two of them, then you
can also answer all of them". I overview some results that suggest that
Specker's principle may be of fundamental importance for explaining quantum
contextuality. Specker passed away in December 10, 2011, at the age of 91.
