Feeling Bad

To feel bad that you are not more Krsna conscious is good if the focus is on Krsna. To feel bad that you are not more Krsna conscious is bad if the focus is on how bad you feel (i.e. the focus is on you). The former is transcendental and the latter is in the mode of ignorance.
Resentment is self-absorption because we are focused on how bad we feel. Manu says the brahmana does not lament (sudra means one who laments). Therefore, Prabhupada says the first qualification of a brahmana is to be forgiving.