What is the danger of polytheism (shirk) in this world and the hereafter?

The danger of polytheism (shirk) is immense; it is an injustice to oneself by worshipping creations, an injustice to the Creator, and an injustice to the people of faith by opposing them. Among its dangers is that it nullifies good deeds and causes its practitioner to fear the unknown and the future. In the Hereafter, shirk is the only sin that Allah does not forgive, and it deprives its perpetrator of Paradise, leading them to Hellfire.