In Wilczek nobel acceptance talk http://arxiv.org/hep-ph/0502113 on page 21 right under equation (2) the interesting question is posed "Why is the proton so light?" It is a Quantum Gravity question, because he is comparing proton to the Planck mass-----the QG scale. In a quantum theory of gravity combining special rel (|c| = 1) and ordinary quantum mechanics (|hbar| =1) with the classical theory of gravity, general relativity (|8piG| = 1) there is a natural scale for any type of physical quantity and you could phrase what he is asking as: "why is the proton only a quintillionth of the natural QG mass unit?" By quintillionth I mean the 10-18 that you see in Wilczek's equation (2). It's nice that, having apparently chosen to have only two equations in the whole Nobel acceptance talk he made one of them this: the proton mass is a quintillionth of QG natural mass. The other equation in his talk, equation (1), is what he calls a "modern embodiment of the ancients' elusive, mystical 'Music of the Spheres'". That part is on page 14. It is a nicely crafted talk for general audience---intuitive and evocative. And he answers the question about lightness posed on page 21: "...The proton’s mass is set by the scale at which the strong coupling, evolved down from its primary value at the Planck energy, comes to be of order unity. It is then that it becomes worthwhile to cancel off the growing color fields of quarks, absorbing the cost of quantum localization energy. In this way, we find, quantitatively, that the tiny value of the proton mass in Planck units arises from the fact that the basic unit of color coupling strength, g, is of order 1/2 at the Planck scale! ..."