Happiness is a mass noun, you can't count it.

'Apple' is a count noun, and you can count it as one, two, etc.

He is receiving countless blessings.

He was counting money all day long.

She looked very happy.

This moment is a fate where everything comes together and feels happiness.

This apple is a countable noun.

A noun is one of the main elements of a sentence.

An uncountable set refers to a set whose elements cannot be counted.

This plan is impossible.