The dark orange goldfish excitedly explains to his light orange friend that he has invented a new board game. He goes over the extremely complex rules to the game and this conversation ensues:
Dark orange fish: Let’s play!
Light orange fish: What do I have to lose?
Dark orange fish: Just the next three days!
This would be a great intro clip to show for opportunity cost / implicit costs. Learning all of the very intricate rules and playing this game will be extremely costly for the light orange fish in terms of the time he has to give up to participate. What else could he do with his time instead?