I love to learn something new, and I'm just as willing to pass on my experience. Writing a tutorial has another advantage for me: to be able to explain even details correctly, I have to go deeper into the subject matter. The finished tutorial can then serve everyone including me as a (hopefully) helpful reference.
The selection of topics depends on its relevance: if several articles already exist on a subject, I don’t have to write another. Common topics are new TYPO3 features, like Routing or the Form Framework. These are supplemented by more general topics of web development.
It is very important to me that these tutorials stay up to date! Therefore I regularly add further aspects of the topic and review changes in new TYPO3 versions.