r-band luminosity fraction of f_∗,halo versus f_∗,disk. Left: Compact ETGs selected from TNG50 central galaxies, colour-coded by the accreted stellar mass fraction f_∗,accreted as indicated by the colour bar, none of these galaxies are strongly stripped. Middle: Compact ETGs selected from TNG50 satellite galaxies, with f_∗,accreted shown with the same colour scheme. Dots and stars denote galaxies with stripped stellar mass fractions f_∗,stripped < 0.1 and f_∗,stripped > 0.1, respectively. We define regions A, B, and C to guide our comparison between simulations and observations. All TNG50 compact ETGs located in region A have extremely quiescent merger histories f_∗,accreted < 0.1, for both central and satellite galaxies. Right: The 15 compact ETGs from observations. Compared with TNG50 analogues, the seven galaxies located in region A likely share extremely quiescent merger histories.