It is inevitable for human nature that man a should wish and seek for happiness, that is, satisfaction with his condition, with certainty of the continuance of this satisfaction. But for this very reason it is not an end that is also a duty. ... It is not directly a duty to seek a competence for one's self; but indirectly it may be so; namely, in order to guard against poverty which is a great temptation to vice. But then it is not my happiness but my morality, to maintain which in its integrity is at once my end and my duty
B. HAPPINESS OF OTHERS,
V. Explanation of these two Notions,
The Metaphysical Elements of Ethics, by Immanuel Kant
Translated by Thomas Kingsmill Abbott
Retrieved from Project Gutenberg
Kant comes from a time that, to my understanding, had no appreciation of psychological addiction. I don't know that he personally ever had the experience of following a routine that you hated, and hating yourself for following that routine, while you are following it. As a person who has had that experience, I can assure you that there is nothing in human nature that makes a search for happiness inevitable. Sometimes humans seek out respite, comfort, or even just fall into routines that we know are injurious to our happiness, but whose allure is overpowering for other reasons.
Kant does make a reasonable argument that seeking personal happiness is not an end which is also a duty in and of itself, but rather, an end which is in service to other ends, and I agree this still holds for things like reducing addictions and altering the behaviors that lead to them. We don't cut back on the metaphorical drinking because the drinking is evil, but because it prevents us from achieving more important things in our life and from having a fuller life.
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