James is saying that the belief that you control your life is an illusion. It’s a Life-Control Illusion. He’s saying: You don’t even know what’s going to happen
tomorrow. There are things you have no control over. You’re like a mist that appears for a little while and disappears. You can get sick, you can get hit by a car, you can get laid off, your marriage can break down, you can die. To think and plan as though you can control your future, James say, is arrogant! If you think you have control and can build your life on your plans, your hard work, your smarts, you are living in an illusion. You are not living in reality.