The internal energy of the body is not constant. In the same body, it can change. For example, if the body temperature rises, then its internal energy will increase, and if, on the contrary, the temperature decreases, then the internal energy will decrease. Also, the internal energy can be changed by doing work. If the work is done by the body itself, then its internal energy decreases, but if the work is done on the body, then the internal energy of the body increases.
One of the components of a person's success in our time is receiving modern high-quality education, mastering the knowledge, skills and abilities necessary for life in society. A person today needs to study almost all his life, mastering everything new and new, acquiring the necessary professional qualities.