Most of the time when you help someone with their research, you have no idea how much you've helped them. Sure, there's the smiles and "thank yous", bobs of the head and hand-shaking, but then the person you've helped (or so you hope) turns and walks away, and you never see them again.
But sometimes you gain a glimpse of your contribution to someone's research, however small or monumental (I'll never forget how I helped a visibly distraught person dealing with their cancer diagnosis--the mere act of showing this person where concrete information could be found soothed their trembling limbs and wiped the tears from their eyes).
I got this brilliant glimpse the other day when I saw this New York Times book review of Charles Bracelyn Flood's new book 1864: Lincoln at the Gates of History. I actually helped do a miniscule bit of research for this man, the library's resident historian, a year or two ago. It was something to do with searching for primary sources from Lincoln's times. I didn't think much of it at the time, just thought it was so cool to read articles written while Lincoln was alive. I make no claims here other than the astonishment of my proximity, however negligible, to this book.
If you're curious to see these articles, just go to the New York Times archives, which go all the way back to 1851.