What they really mean: Sans suffers nonstop no matter what you do. Even if you only do a pacifist run and leave it with the true ending and never reset, he still lives through and remembers the timelines and resets of all the other players of Undertale and he is never truly happy because of this. But he ignores it and makes terrible puns with Frisk and Papyrus, eats and compliments his brother's spaghetti even though it's terrible, and he always smiles and acts like he's fine. And he thinks the world of Papyrus, constantly going on about how cool he thinks he is and he actually means it. Sans is just an amazing brother and endures so much pain while still managing to provide comic relief throughout the game based on how you play and he's just so strong and brave and I love him