Only actions done from duty have genuine moral worth

Kant draws a sharp distinction between an action that merely conforms to what duty requires and an action performed specifically because it's required by duty. A shopkeeper who charges fair prices only because honesty is good for business is acting in accordance with duty, but Kant denies this act any real moral worth, since the underlying motive is self-interest, not respect for the moral principle itself.

His famous illustration involves comparing someone who helps others because they naturally enjoy it to someone who helps despite no such inclination, purely because they recognize it as their duty — Kant controversially argues the latter case reveals moral worth more clearly, precisely because inclination isn't doing the work; only the recognition of duty is.

This isn't a claim that natural sympathy is bad, but that moral worth, strictly defined, must be traceable to the will's respect for a rational principle, not to any accompanying feeling, however pleasant that feeling might be.

Takeaway: doing the right thing because it feels good doesn't yet demonstrate moral worth — Kant reserves that specifically for acting from recognized duty.