Stellar tracks for a 25 M_⊙ star. The upper panel shows a rotating star with Ω/Ω_c = 0.6 for three different metallicities Z = 0.002,  0.003,  0.004. The lower panel shows a star with metallicity Z = 0.003 for three different values of the initial rotation speed Ω/Ω_c = 0.5,  0.6,  0.7. The linestyles and color code are the same as in Figure 1. The vertical dotted black line represents the temperature below which we expect the bi-stability jump. This Figure shows the non-monotonic dependence of mass-loss on metallicity and rotation. Low metallicity (Z = 0.002) favors the activation of optically thick winds through channel 1, because the star is more luminous and compact. Higher metallicity (Z = 0.004) can also activate optically thick winds through channel 2. Stars in the intermediate metallicity case (Z = 0.003), instead, fail to activate optically thick winds soon enough and end up as cool supergiant stars. The same trend happens for rotation.