The thanks you feel and never say does nothing for the person who earned it.

We assume people know. Your mother knows. Your colleague knows. Your husband knows. They do not know, they suspect, and suspicion is thin nourishment for anybody.

Be specific, because general praise slides straight off. Not you are amazing, but you covered for me in March when I was falling apart, and I noticed. Detail is what proves it.

Specific gratitude lands differently. It shows you were paying attention, which is the actual gift, and they will remember your sentence long after they forget the favour.