Karbala is the cruelest tragedy humanity has ever seen. Yet, the startling (though appalling) events in Karbala proved like a powerful volcano that shook the very foundation of Muslims, it stirred their consciousness, ignorant or learned alike. For sincere Muslims, Karbala turned into a triumph. The tragic event became the very beacon of light to always remind Muslims to practice Islam honestly and sincerely, to do what is right irrespective of consequences, and fear no one except Allah (swt).
On the other hand, Yazid never achieved what he and his father had planned to achieve, for within three years, Allah's wrath fell upon him, causing him to die at the age of 33 years. And within a few decades the rule of Benu Umayya crumbled and came to an end. The tragedy of Karbala taught humanity a lesson that standing for the truth and fighting unto death for it is more honorable and valuable than submitting to the wrongful, especially when the survival of Islam is at stake.