Over-thinking ruins you. Ruins the situation, twists things around, makes you worry and just makes everything much worse than it actually is
Imagine if Sam is the Tower's designated chef because he's the only one who knows how to make food that is both good and nutritious (honestly Steve you can't just boil everything). While everyone has been eating his cooking enthusiastically, he can't help but notice that Tony doesn't eat much if at all. He started being concerned about Tony and try to find something that Tony would enjoy eating. Somewhere along the way he realized why he cares so much about Tony.