don't let your guard down after a victory; tighten your helmet strings after winning
Proverb warning against complacency after success; literally 'after winning, tighten the strings of your helmet'.
Just because we won the match, let's approach the next practice with the spirit of 'don't let your guard down after a victory.'
A traditional Japanese proverb derived from samurai culture, where a warrior was advised to retighten his helmet cords after a battle to stay prepared for unexpected attacks.