Part of the point is what 'better' now or later means, and what the point would be in making a decision in the face of the given optimum.

The earring is always telling you to do 'what will make you happiest.' How do you make a decision between 'happiest' and literally anything else? You will 'always regret it' if you do something other than what the earring recommends. Do you think there is anyone in the world, living or dead, who, when faced with the reinforcement conditioning of pleasure and satisfaction when doing one thing and dissatisfaction when doing something else, could maintain, long term, a sense of even the possibility the choice that makes them happy could be the wrong choice?

It ultimately ends up in the same place as many other questions like this. Blissful ignorance or painful freedom? Shall one live in pursuit of pleasure or can there be something of greater value in identity and autonomy?

Personally, I also wonder about its limits. The earring simply tells you what will make you happiest, but there are often situations where your options are extremely limited. If you were stripped of all possessions and left in a foreign land with nothing but the earring, could it tell you to do anything but lay back and go to your happy place while you wait to die? If you are any of the people in our world with less fortunate starting points, could it do anything that wouldn't be actually still worse than the average level of enjoyment for an average person? It doesn't make you happy, just the happiest you can be for now.