Say the compliment out loud. The nice thoughts you keep to yourself help nobody.

A good opinion kept inside your head has no effect on anybody. You notice something true about a person, decide it would be awkward to mention, and the thought evaporates while they go on with no idea it existed. People are consistently wrong about how this lands, assuming it gets brushed off when in fact it gets replayed for years. The price is roughly four seconds of mild awkwardness.

Say three of them this week, out loud and specific. Not nice shirt, but something about how they handled a situation or what they are genuinely good at. Then watch what it does.