Full Idea
Being consists not in what it is already, but in what it is not yet, a being that consists in not-yet-being. Everything else in the world is what it is….Man is the entity that makes himself….He has to determine what he is going to be.
Gist of Idea
For man, being is not what he is, but what he is going to be
Source
José Ortega y Gassett (Toward a Philosophy of History [1941], p.112,201-2), quoted by Kevin Aho - Existentialism: an introduction 4 'Problem'
Book Reference
Aho,Kevin: 'Existentialism: an introduction' [Polity 2014], p.49
A Reaction
[p.112 and 201-2] This seems to be Ortega y Gasset's spin on Heidegger's concept, by adding a temporal dimension to it.