I'm not just referring to humans, we are certainly the most sadistic of creatures, far too often deliberately, often taking pleasure in others pain. I also think about the Animal Kingdom in which instinctive responses or need to sustain oneself requires hunting and eating other creatures. I've heard some strong explanations such as "we need evil to know what good is" etc. However, the abundance of suffering, just the physiological system of nerves and sensors that elicit pain, it's always been difficult for me to understand why God created earths creatures this way. In fairness, I don't even know why this makes sense from an evolutionary standpoint either when I think are probably better ways to have been built (even as the human body and brain is the most complex on earth).