Human behaviorists believe that the brain has two common modes of operation, the left brain mode and the right brain mode. All of them operate in these two modes, but they are inherently biased toward one of them.
When the two hands are crossed together like this, according to the theory, if the right thumb is above the left thumb, then your inclination is the left brain person, good at language expression and rational analysis of things, if the left thumb is Above the right hand thumb, your tendency is the right brain person, may be good at visual creative and intuitive work, so you are left or right brain.