I started thinking about my dumb luck picking Drupal as a tool about 9 years ago. I was looking for a Content Management System that made sense.
I was awfully interested in a project called PAWS (PHP Automatic Web Site) -- and it's a good thing I didn't ride that horse, which was long ago put out to pasture.
A client asked me to convert his static PHP site so that he could manage the content in the include files without editing code. I built my first Drupal 4.x site, with the crazy hack of creating a node for every include, and then printing the includes/nodes inside a main node (Panels, sort of, which did not exist in Drupal then). I also customized the front end of the TinyMCE wysiwyg editor to add buttons to apply his brand's pink and blue colors. The client smoked a lot of pot, drifted away, came back a year or two later for more work -- without a database. Oh well, not the first - or last - time the db was lost by a client.
That experience convinced me that a lot could be done with Drupal that I had not been able to do without a lot of custom coding just to build the base web application. Other projects with early versions of WordPress and Mambo (predecessor to Joomla) left me unimpressed with their extensibility. I have often said since then that "WordPress is like the smaller sibling of Drupal, but Joomla is the evil cousin."
Then Earl Miles conjured up his merlinofchaos wizardry for Sony Music, creating Views and Panels and Ctools, and that was around the time that a lot of developers took notice of Drupal. I was profoundly convinced that Drupal had outgrown being a CMS enabling writers to (more or less) easily edit content without (much) coding, and had become a Content Management Framework that could perform elegant and dynamic manipulations of the content in its database.
So I had to add dumbluck to my mentors - not just for my early experiment hacking the node system, but for each solution that I was able to implement afterwards, because my choice of Drupal provided me with an extensible framework allowing complex algorithms for presentation of content, and the Drupal project improves with every contributor's enhancements.