This reminded somehow of other word, with other meaning, "unforgiving":
We weren’t crossing the Rockies; still, we recognized that for pilots unaccustomed to operating at higher elevations, the flight environment can be very unforgiving of poor planning. (...que não perdoa planejamento "meia-boca").
Mountain flying ~ opens up new opportunities for the general aviation pilot for unique and interesting destinations, plus a view of spectacular scenery. However, mountain flying, even more so than flight in the flatlands, is very unforgiving of poor training and planning.
(...é implacável com planejamento e treinamento e planejamento insuficiente.)
Yet, for the unwary, unsuspecting or uninformed visitor, the Sonoran Desert can be an unforgiving place. A small blunder can turn an afternoon drive off road or an overnight camping trip into an emergency. People sometimes die in the desert.
(Contudo, para o visitante desavisado, confiante e desinformado, o deserto de Sonora pode ser um lugar implacável...)
I brought that to the table, so the learners can compare them. But they have different meanings, be aware of that.