1. If it is an illusion, you shouldn't treat it as a truth. Vice versa.
2. It's like the equation of plus minus operation in math, only a special case one explained;
if - meets +, it becomes -
if + meets -, it becomes -
if + meets +, it becomes +
ignore if - meets -, because it's an error in real life.it wouldnt become +3. You know what to do.