How can we define a self-portrait?

It seems that the concept of a self-portrait has a varied response, giving a varied perception on what a self-portrait actually is. Looking at some of the self-portraits in lectures, using thorough analyse, we can clearly identify the purpose of the self-portraits, giving the idea that a picture really can say 1000 words. But, is it possible that in our curiosity, we often over complicate and are too thorough in our analyse of these 'self-portraits'. I felt that the image of Rembrandt, aged 22, was a clear example of how we can often overlook the point behind the self-portrait. I straight away believed that the man was deranged and crazed. When in actual fact, he was only practising his drawing skills. I believe that a self-portrait represents a connection or link between the artist and the piece of work. Although, this connection could be the tiniest of things, often, it portrays a bigger picture to the artist and viewer alike. Giving a clear portrayal of who the artist really is inside, in oppose the person we see on the outside.