Kant said, 'Act only in accordance with that Maxim through which you can at the same time will that it become a universal law.'
This is not only a brilliant reconfiguration of the Golden Rule: treat others as you want to be treated, but an improvement on the idea of platonic forms. On one level, it says that which you put into the world will never reach a point by which one can say it never happened. It remains forever a model one can recreate in the future. It doesn't matter if an action or form exists because of a presupposed universal blueprint. Where Kant and Plato before tend more toward an imperative on nature from the top down, reality is closer to the esoteric view: that the imperative is gestational and represents the limit of what is possible (or even the endless infinity of what is possible). Nietzsche tried to do Kant one better but really just poeticized the same idea when he said, 'Act as though you would be willing to repeat that action an infinite number of times.' The idea is that, if it's happened once, it has happened before and will happen again. To modify it with the help of Plato and Kant, one can say that there could be a better version of your action or creation in the future and that, perhaps, the tools to build it are in the past.
Now, there may not be some literal cast or mold projected into the universe by your actions, but you are nevertheless carving out a space of possibility. All of our actions have effects which reach indefinitely into the future even when others don't ever see them, just as the whole phenomenal world is locked into a set of causes and effects we can't always see. In a way, Kant is right or can be made right. Your every action may not become universal law, but then, it might become a self-perpetuating pattern which survives you and your successors for years to come and which others will inherit. In the east, this is called 'Karma.' Karma doesn't have strictly to do with reincarnation. The people of ancient India understood its underlying principles: we are all part of the universe and, therefore, have the duty to act in a way that creates harmony.
One doesn't need to believe in Karma to understand the concept and apply it to life. Kant's categorical imperative , if viewed in a gestational manner, takes up the same project. It is the opposite, in a way, from solipsism, in that it posits that everything inside gets put into the universe; a view approximate to the instruction Arjuna received in the Bhagavad Gita that actions must be offered up as a gift in order to remain free.
It's a way of making one aware of one's place in the universe and the importance of realizing one's role.