Often someone who has stopped smoking will rapidly gain 5 to 7 pounds and then lose it very slowly. A few will gain a greater amount when they stop smoking.
It takes time to develop the feeling of satiety, and probably those individuals who tend to overeat when they eat rapidly would eat less food if they ate more slowly.
Your weight is largely controlled by your brain's weight regulating mechanism called the "fat thermostat". The setpoint of this fat thermostat influences your appetite, your energy and your level of weight.
The excess weight in an obese person is due to fat. Adipose tissue is over 80% fat, but there is some water and protoplasm found in fatty tissue. When losing excess weight there is very often water retained in the body in that space freed by the disappearance of fat.
Your motivation to research weight loss psychology probably comes from a need or desire to weigh less, look and feel better than you now do. At this point you may be very aware of the problems associated with excess fat.