Shunryi Suzuki was once asked why there was so much suffering. He replied, "No reason."
Humans try to hard to attribute the good/bad of life to "something". Stuff happens, that's all. The only thing we can control is our action and thoughts. If we choose to practice cultivating actions and thoughts that benefit instead of hurt, the result (karma) will manifest.
1. All that we are is the result of what we have thought: it is founded on our thoughts, it is made up of our thoughts. If a man speaks or acts with an evil thought, pain follows him, as the wheel follows the foot of the ox that draws the carriage.
2. All that we are is the result of what we have thought: it is founded on our thoughts, it is made up of our thoughts. If a man speaks or acts with a pure thought, happiness follows him, like a shadow that never leaves him.
Dhammapada