From the movie Changing Lanes. Ben Affleck talking to Samuel L Jackson.
— and then, magically, this whole incredible day just somehow becomes a memory. It's like you go to the beach. You go down to the water. It's a little cold. You're not sure you want to go in. There's a pretty girl standing next to you. She doesn't want to go in either. She sees you, and you know that if you just asked her her name, you would leave with her. Forget your life, whoever you came with, and leave the beach with her. And after that day, you remember, not every day, every week. She comes back to you. It's the memory of another life you could have had. Today is that girl.
It's a just metaphor. There never was a girl. Well, there might have been but it's not really what this is. It's about this day — today — when after all the thinking back and imagining, he finally changed his life.