To motivate

Research by, among others, the American neuroscientist LeDoux shows that learning is strongly influenced by emotional processes. That's because those processes activate the plasticity of the brain, changing neural networks and forming new ones. Depending on whether such a change creates positive or negative feelings, it strengthens or weakens the motivation for that particular subject. This is clearly visible in the increasing or decreasing motivation of students for mathematics. Depending on whether they think they are good or bad at it, their motivation increases or decreases.
Such an emotionally driven change in the brain is clearly visible in a brain scan. For example, with an 'Aha reaction or Eureka moment', when the subject suddenly gains a new insight and becomes aware of that understanding.
Encouragement and praise from teachers produce two effects. First, students behave in such a way that a reward comes into view. Their motivation increases and they show greater task orientation. Dopamine also ensures that they feel comfortable with it.
Second, adolescents often work not for the content of a subject, but for the man or woman who teaches it. The compliment is perceived as a reward in itself. The reward does not even have to be concrete, as long as a student associates the situation with reward. For example, learning can be improved by making the lesson material challenging. When a student learns something new and masters it, the reward is the achievement he has made.
Another way to improve learning is to build in humor. Humor is also not an explicit reward, but during laughter endorphins are released in the brain and this has a positive effect.'

A pleasant lesson on during the day can ensure that students look forward to the next lesson with positive expectations. Pleasant feelings are just one of many emotional responses elicited during the average school day. Annoying or negative feelings are often caused by emotions of fear or anger. These negative emotions are prioritized in the brain over emotional responses such as pleasure. The example of a class looking forward to the next lesson can therefore easily turn into a situation where both the students and the teacher drag themselves into the classroom with negative expectations.
Rewards don't have to be concrete to reinforce learning. When learning something new, the challenge and feeling of accomplishment is the reward. Conversely, learning can be inhibited, as threatening punishment increases disgust for a particular subject.
The result is that 'positive' motivation is reinforced by a possible reward, while aversion, or negative motivation, is reinforced by the threat of punishment.