Many writers will tell you that they build their characters from people they know, have met or have observed and eavesdropped on out in the wild.
Not long ago I had the opportunity to sit in a chain coffee shop far from home for several hours. I spent it observing the many people coming and going - discreetly, I wouldn’t openly stare as I was bent over my notebook most of the time.
I would imagine what their lives were like based on various clues I picked up about the clothes they wore, the way they used their cell phones, how loudly they would share information with the barista - you’ll note people will either say something for which they want sympathy or praise - what method they would use to pay for their beverage, how they talked to their kids, etc. You can learn a lot about a person just by observing.
One individual in particular stood out.
The more I listened in on his conversation with someone he had just ‘recruited’ for his ‘how to build true wealth’ program, the more he started to sound like the archetype conman, the trickster.
Since he had set up shop at a table behind me, I made a point of not looking around and only listening. Piecing together the clues from only sound, such as the nervous shuffling of paper when his latest recruit told him about a stint in prison. The rushed breathing and hurried talking when he realized he was losing his recruit’s attention.
The story as it unfolded was fascinating - for a writer - and using deductive reasoning and a very active imagination, I filled in the blanks of how this story would unfold based simply on an overheard one hour conversational sales pitch. In my story things did not end well for the trickster and judging by the way he rushed out of the coffee shop I suspect he may have thought that as well.
I imagine spies use similar techniques to piece together information and puzzle out stories, but instead of a high level, secret report, this story might end up in one of my books one of these days.