Motivation is by definition intrinsic. In other words, motivation is an intrinsic mental mechanism, because motivation always comes from the person himself. Intrinsic motivation is therefore a pleonasm. They are external factors that strengthen or weaken
motivation. Learning always needs motivation, but external factors determine the degree of motivation.
Whether it's the just-survived encounter with a cave bear or the great story of the history teacher or the razor-sharp criticism of the English teacher or even the ideal for which you want to give your life; they are external factors that trigger the mental process of motivation.
Adolescents can get into a 'flow' for a subject that touches their heart and know a lot about it in the shortest possible time. The 'flow' itself can be the reward here, but also the appreciation, recognition or admiration of others. A powerful motivating factor is the 'eureka moment'. Suddenly someone sees the solution to a certain problem. The brain reacts very positively to this. Learning would benefit from consciously incorporating elements into the curriculum that give students the opportunity to experience such moments. This can be done at different levels and it should be done as early as possible in education. 'Eureka moments' are addictive. Once a person has experienced it, it strengthens the motivation to get that feeling again.
Adolescents are extra sensitive to these kinds of factors, but the disappointment when it doesn't work out is all the greater. Adolescents must learn to deal with disappointments. For this they need not only help but also guidance from adults.