Our plans miscarry because they have no aim. When a man does not know what harbour he is making for, no wind is the right wind.
errant consilia nostra, quia non habent quo derigantur; ignoranti quem portum petat nullus suus ventus est.
Original text (Latin)
Notes from Wikiquote
Line 2
Variants
If one does not know to which port one is sailing, no wind is favorable. (translator unknown).