Keep it short and to the point

A great book is a great evil

That is to say, a long book is likely to be verbose and badly written. The saying is recorded in English from the early 17th century but is found earlier in Greek in the writings of the Hellenistic poet and scholar Callimachus (c.305–c.240 BC) as ‘the great book is equal to a great evil.’ [Méga Biblion, méga kakón]

It reminds of that saying "Brevity is the soul of wit" (from Hamlet).