From real life, of course. From experience. From melding and molding the personalities we meet along our journey to develop our characters. Maybe we exaggerate their quirks a little (or a lot), but it all starts with a solid base in reality.
Same with settings. This is Herb's Bar. Herb's is an integral part of the series. There was a bit of fudging going on during the writing, the owners are different, changed to Gertie's nephews. But every silence when the door opens while the customers size up the new guy - that happens. Without fail. The music playing when Gertie stomps in is the same as you'll hear if you go there.
And just like in the book, nobody can remember anybody named Herb ever owning the place.
Bars like Herb's are where the action happens in our small towns. It's where the locals have a beer together in the late afternoon, then skedaddle before the younger bunch arrives. It's where Gertie pumps customers for information and grills Red and Ed (her nephews) about strangers and what they might have overheard from the working side of the bar.
So next time you're in the Michigan U.P. and you drive past a place called Herb's (hint: it's on M35), stop in for a cold one and tell them Gertie and Deb sent you. You may even meet this guy.