Hertzsprung-Russell (HR) diagram showing stellar models from the standard set colored by the maximum of L_rad/L_Edd (left panel) and the minimum of P_gas/P_total (right panel). The blue cross marks the end of core hydrogen burning and the red cross marks the end of core helium burning (where applicable). The brown dashed line in the left panel denotes the position of the observational Humphreys & Davidson (1979) limit beyond which few stars are observed, while the gray dashed line signifies the luminosities of the brightest red supergiants as inferred by Davies et al. (2018). Large values of L_rad/L_Edd and small values of P_gas/P_total in the envelopes of stars with initial masses 30 M_⊙ and above causes the evolution of these stars to become halted at log T_eff/K ≈ 3.7, and their models fail to even finish core helium burning.