I can’t recall ever wanting to do anything other than scientific research. I found it interesting to hear about, and I liked the idea of finding out for myself what the laws of nature are, and how they work.
I do remember the moment when I decided specifically to take up physics. It was when I found out what physics is, during my first few physics lessons in school. Interestingly, those first few lessons involved little or no actual physics, theoretical or practical. They were all about the kind of thinking that is used in physics, and as far as I can recall, consisted mainly of stories.
David Deutsch is author of The Fabric of Reality (buy this book from Amazon (UK) or Amazon (USA)). See his website.