Clarity

Euripides, Orestes 397 (tr. David Kovacs):

Clarity is the wise thing, not unclarity.

σοφόν τοι τὸ σαφές, οὐ τὸ μὴ σαφές.

C.W. Willink on οὐ τὸ μὴ σαφές:

the 'pleonastic negative converse' (a common idiom for emphasis, cf. 613-14*; Bruhn 118-19) became something of a mannerism in late E., cf. IA 93, 916.