One of the things I learned, one of the strangest things, is how to think. - Abraham Pais

Progress leads to confusion leads to progress and on and on without respite. Every one of the many major advances … created sooner or later, more often sooner, new problems. These confusions, never twice the same, are not to be deplored. Rather, those who participate experience them as a privilege.

Deliberately or not, every author is of course present in every book he or she writes - even in a scientific text.

To make a discovery is not necessarily the same as to understand a discovery. Not only Planck but also other physicists were initially at a loss as to what the proper context of the new postulate really was.