There's no question that the convincing was gradual. Deep inside, I sensed something was wrong with Islam and god, but obviously I didn't even try to investigate this. If I encountered something that didn't make sense, I magically rationalised it away (which was very often). Funnily enough, before this discussion with my friend, I always considered myself an open-minded Muslim (I snort at this now, because it was a mere delusion), but when my friend brought reason to the table, I naturally became defensive. This defensiveness slowly, but surely, turned into silence. He made far too much sense, time and time again. The dawn of realisation that god didn't exist, however, was sudden. And it makes me smile thinking back to that moment :)