In Psychology Today, acceptance.

Gelassenheit has not only been embraced in religious contexts. From a more secular perspective, Martin Heidegger portrayed it as a stance of nichtwollen (non-willing), of not straining against fate and the currents of life9. This doesn’t mean acquiescent passivity or pessimistic fatalism. As per the ‘commitment’ aspect of ACT, existentialists like Heidegger still emphasise the importance of acting boldly upon our values. It just means recognising that much of life is outside our control, and even to an extent pre-ordained, with causal chains always already in motion, influencing future events. Qué será será, as the saying goes, what will be will be.