French to English Marketing Law: Contract(s)

A quote from Leonardo da Vinci. Obviously drummed into kids in French schools to reinforce the virtues of preparation because it comes up a lot.

Context : advice to monitor and keep ahead of what the competition is doing by way of advertising.

I am looking for a canonical English version, if such exists. I think I understand its meaning, so a gloss is not required. I would be grateful to hear from any of the learned folk out there who might know how it appears in a dictionary of quotations or a list of aphorisms, etc