Having been a programmer for more than 8 years now, I feel I still cannot grasp the functionalities that would make the end-users happy. These might be a mere few lines of code from a technical perspective, but these might very well make the end-users very happy.
I came across one of such incident recently. One of the user of my application was an elderly person who had to type in so many numbers from one system to a third-party system (among many tasks). So, we added a “Copy” icon for her to copy those numbers on a button and simply paste them in the other system. I was really amazed by her gratification. And it made me realize no matter who complex algorithm or architecture we design for our customers, it won’t matter until it helps them in one way or the another.