A: Hurry up! We are going to be late. This party is my big chance.

    B: Relax. It’s just a party thrown by your millionaire uncle. No big deal.

    A: Come on! And lots of musicians. I’m a bit of a rocker myself, and this might just be my chance to meet someone famous. Maybe I can join a band. Come on or I’ll miss the boat!

    Note: This idiom means to “lose an opportunity to do something by being slow to act.” Boats have a schedule. If you want to go on the boat, you must get there on time. If you are late, you miss the boat and will be disappointed. The metaphor is having missed some kind of opportunity that “left the dock” before you could get there, or before you could make up your mind. Sometimes the expression, “The train has left the station” is used similarly to say that you’re too late. After all, opportunity knocks but once.