What is spirit?

a spirit is are dead humans life being put into heaven or hell

SPIRIT:

By default our muscle tone is 50%. If it become less than 0%, then postural reflexes reset it to 50%.

If we have uncontrollable fear that makes us tremble, it indicates that the muscle tone is frequently becoming less than 0%.

COMPETITIVE BLOCKADE:

If two thoughts try to enter our conscious mind, neither of them succeed and this resets the mind, makes it blank and muscle tone 50%, which is the default value.

A dead man would have the lowest tone. We can block our extreme fears with the muscle tone of a dead person. The tone of a dead person is selected because quantitatively the two tones are the same. Precise timing is necessary to make the blockade successful. If done successfully, we would neither have extreme fears nor the tone of the dead person. What all we would feel is the normal 50% tone.

However, if the blockade fails, then the dead person would cause extreme fear in us and may even control all of our activities. Then we would be said to be possessed by the spirit of the dead person.

Thus, spirit is anything that restores our muscle tone, insufficient to maintain posture, to normal, by competitive blockade.