  It is often claimed that 98% of the nucleon mass is generated by quantum
chromodynamics. The decomposition of the nucleon mass based on the trace of the
energy-momentum tensor suggests that gluons play by far a dominant role. About
25 years ago, Ji proposed another decomposition based on the energy component
of the energy-momentum tensor, leading to a quite different picture. Recently,
we critically revisited these decompositions and argued that both overlooked
pressure effects. In particular we showed that Ji's decomposition, although
mathematically correct, makes little sense from a physical point of view. We
identify the proper mass decomposition along with a balance equation for the
pressure forces.
