It is difficult to continue at the point of perfection, and naturally that which cannot advance must recede.

Difficilis ... in perfecto mora est, naturaliterque quod procedere non potest, recedit.

Original text (Latin)

Notes from Wikiquote

Historiae Romanae, I, xvii, 6

Quote text and notes from Wikiquote: Velleius Paterculus (page history), available under CC BY-SA 4.0. Source quality and labels are our own summary of what Wikiquote records.