Origin of dynamically hot orbits as a function of stellar mass. All central galaxies in TNG50 are encompassed. The solid black curve depicts the overall luminosity fraction of hot orbits in galaxies at z = 0, consistent with the CALIFA galaxies from observations (red dashed). The blue, yellow, and red curves indicate the contribution from in situ stars born cold, warm, and hot, respectively. The dashed curve represents the contribution of ex situ stars. The shadow areas are the 1σ scatter of galaxies in each mass bin.