Research, yeah that's it!
I sometimes amuse myself when it comes to putting details in my story. When I first started writing "Downtime", I decided Fury needed a car when he visits Tony Stark. But since, in my ficverse, the original version of SHIELD is answerable to the American government I decided I needed a car other than the modified Ferrari 330/P4 Berlinetta from the first Nick Fury: Agent of SHIELD series. I wanted a 60's American sports car that would be a good replacement for the Ferrari (expensive but cool)-
I ended up giving Fury a red 427 Shelby Cobra. (Mostly because the most expensive American sportscar ever sold at auction was a Cobra for $5.5 million dollars last year.)