Back in the days when writing had rules, one of 'em was "Write what you know"
Since I don't know what it's like to be blind in the 19th century or a thief in any century, I've always taken this to be mostly about creating realistic characters before putting them in situations we imagine. Of course research helps. Digression: recently read a blog where the author suggested that skipping research is better for the story. I wept.
That said, do we always remember all the people who've influenced our characters? I thought back to all the guys I considered attractive since I was old enough to have those thoughts.
Then out of the blue, I remembered Gerald. He was two grades behind me and I didn't have a crush on him, I just thought he was pretty. Until seeing him, I hadn't known boys came in pretty. He had big brown eyes and dyed blonde hair that fell across his eyes. With dark roots, and a casual, constant swipe at his hair, he was just adorable. I eventually dug out my yearbook to look him up; my memory is kinder than the yearbook photographer.
I guess he came to mind because I started writing younger male characters, prettier male characters. And I was drawing on my memories of him to "write what I know."