Full Idea
Our happiness is the only thing of importance, provided this is judged, as reason requires, not according to transitory sensation but according to the influence which this contingency has on our whole existence and our satisfaction with it.
Gist of Idea
Our happiness is all that matters, not as a sensation, but as satisfaction with our whole existence
Source
Immanuel Kant (Critique of Practical Reason [1788], I.1.II)
Book Reference
Kant,Immanuel: 'Critique of Practical Reason (Third edition)', ed/tr. Beck,Lewis White [Library of Liberal Arts 1993], p.64
A Reaction
This is closer to the Greek eudaimonia than to the modern conception of happiness, which is largely just a feeling. Kant's view seems more like a private judgement on your whole life, where the Greek idea seems more public and objective.