Duhkha
duḥkhaSuffering, or unease: the problem the whole tradition is answering.
The Sutras make a sweeping claim that sounds pessimistic until you read it closely:
To the discriminating, all is, as it were, painful on account of everything bringing pain either as consequence, or as anticipation of loss of happiness, or as fresh craving arising from impressions of happiness, and also as counteraction of qualities.
The original Sanskrit
pariṇāmatāpasaṃskāraduḥkhair guṇavṛttivirodhāc ca duḥkham eva sarvaṃ vivekinaḥ
Everything carries pain for the one who has learned to look: getting ends in losing, pleasure trains craving. And then, in the next line, the tradition's whole optimism in eight words:
That which is to be escaped is pain yet to come.
The original Sanskrit
heyaṃ duḥkham anāgatam
The misery that has not yet come can be avoided. Practice exists because of that sentence.