What are Particles?

As I continued to read the biography on Paul Dirac, The Strangest Man by Graham Farmelo, I came across this very ensightful quote of Dirac's which gives a very good sense on how we can imagine particles.

When you ask what are electrons and protons I ought to answer that this question is not a profitable one to ask and does not really have a meaning.  The important thing about electrons and protons is not what they are but how they behave - how they move.  I can describe the situation by comparing it to the game of chess.  In chess, we have various chessmen, kings, knights, pawns and so on.  If you ask what a chessman is, the answer would be [that]  it is a piece of wood, or a piece of ivory, or perhaps just a sign written on paper, [or anything whatever].  It does not matter.  Each chessman has a charateristic way of moving and this is all that matters about it.  The whole game of chess follows from this way of moving the various chessmen.

Source: Farmelo, Graham. The Strangest Man. Basic books, Philidelphia, 2009.