Shoot for small victories. Keep your eyes and ears open and you will see the payoff for the small victories. For example the last day I was at work SL was a hot mess. I knew I couldn't get it up to par by the end of my shift, that it would still be a hot mess when I left. I was folding a table of men's shirts when a woman walked by me and said "Thanks (not my name but starts with the same letter)" as she walked past. I was scratching my head for half an hour on that one, and then I realized that she had been the woman in the aisle looking at the swimsuits facing the aisle while I was putting the swimwear reshop away. She had been complaining about the lack of modesty the tops had, since she was going to be taking her kids with her she didn't want risque. I had grabbed a top that was more of a tube than two triangles and showed her and she said that cut had been what she was looking for. So small victory, I found what she wanted, I made the store a sell, and she remembered me even when I was crouched down, my nametag hidden by the table, folding a shirt on the bottom.
I think it's human nature to not realize how much "Thank you" is needed. We feel it and we just think it's obvious to the other person, so the words themselves might not get said. If a coworker always seems happy when you get in though, obviously whatever you are doing at work matters to that person, even if the words were never said.