I grew into my fandom in through the 80's, with it really coalescing in 1989. And there is no doubt that Sandberg was my favorite athlete throughout those years and into my teens. I don't have many of my old baseball cards, but I still have a long box of just Ryno cards, including multiple rookie cards I saved up to buy in my tween years. I have an OG Sandberg jersey, had Sandberg posters on my walls, and in LL/Babe Ruth league I tried my best to emulate his batting style.
He has since been eclipsed as my favorite Cubs player ever by flashier players, but Sandberg was a central figure in my growth into a Cubs fan. Beyond the fact that the passing of a childhood idol is also a reminder of my own mortality, it's one less living link to my childhood, and a huge bummer.