These days you will never find me without some form of writing implements. When I sleep I have a phone and most of the time a notepad next to me with pen at the ready, when I walk I have a notepad on my phone or a piles of papers or receipts shoved into pockets purely to be written on when needed. All to prevent an idea from ebbing away and disapearing before it can be captured.
Ideas can come from anywhere, the way the sunlight looks through an oddly shaped tree, how a feather falls in the air, a fragment of misheard conversation, a car parked at an unusual angle. Some writers like to hope that the idea will be strong enough to remain within their head until it has evolved into a fuller story, others like me will write every little idea down. Over the years I have developed a slightly obsessive habit of writing things that interest me or pull at a spark down, I will openly admit I do so because I'm scared if I don't it will leave and never come back. That isn't anything to do with the idea itself but more my past and a distinct lack of remembering things, I really do envy those who can hold those ideas in their heads until they have evolved - I just am not one of them.
In one of my other jobs I have begun to notice how people can be obsessive in other ways, which is a relief to know that writers aren't the only obsessive nuts out there! These obsessions can be little things, pencils having to be straight before writing, always having certain items on people and constantly checking that they are there to always going to the same coffee shop ordering the same drink and sitting in the same seat (I have to put my hands up here and admit I do this one possibly too much then I should but I can't say no to a good coffee).
I do sometimes wonder what people who don't know me think when I walk past them noting things down on paper, or when they walk past as I'm in the coffee shop and suddenly jump to attention to feverishly take notes. I have learned the hard way that obsessions can take over your life, but some like note taking when ideas hit can be useful and helpful especially when your job is centred on ideas. So this is one obsession I will definitely be keeping for as long as I can.