It is important to define humanism first and then offer an opinion.
Although humanism can be defined in many ways, I would say that humanism is at root a worldview that values human concerns rather than divine matters. It first emerged around the Renaissance and continues until today, mostly in intellectual circles.
In my opinion, human has failed for two reasons.
First, many people thought that religious matter would naturally disappear with the advancement in knowledge and science. Religion was thought to be an odd and unnecessary vestige from the past. However, if we look at it today, there is an explosion in the area of religion. People are extremely religious. The next war may be over religious ideology. Hence, religion and religious issues are of paramount importance.
Second, humanism usually also has an idea of the goodness of humanity. The buzz word before World War I was the brotherhood of man. This was quickly dashed in view of two World Wars. Moreover, when we view the atrocities of the world even now, many people do not see a brotherhood of people. We need to deal with the evils that people commit against one another. This fact has weakened humanism to a certain extent.