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If you want to live long and have peace of mind in life, try not to understand everything.
There is no point wasting your energy trying to figure why things happen the way it did, just accept it and move on. No matter how hard you try, you cannot understand everything in life.
Do your understand how you use your phone to communicate with another person that is far away from you? But you still make the call anyway. Do you understand how plane is able to fly in the air? But you still enter the plane and fly.
Don't try to understand people too much, always want to figure out why they treat you the way the did. Just move on anyway and fly.
Don't try to understand everything.