When you step back and realise that you've written more than 20,000 words worth of SSSS fanfiction, and you're still coming up with ideas for new stories.
And when you're looking at the module catalogue for your final year at university and get all excited because you might be able to take beginner's Swedish - despite the fact that, had you asked me if I wanted to learn Swedish a few months ago, I would have laughed in your face.