What actually breaks down between the site visit and the customer saying yes?

Quoting seems like it should be the easy part, but it keeps coming up as where solo guys lose the job or leave money on the table.

For those running your own book: what does your process look like from the time you leave the site to the moment the customer confirms? Are you writing it up that night, next morning, back at the truck?

And where does it most often fall apart, the pricing itself, the follow-up, getting paid once they do say yes?