To capture is to become in the possession of. To capture a moment is to capture the memory of something and be able to look at it when ever you please. To capture someones attention is to hold their view and interest, and be able to make them lose interest when ever you want. To capture is to become in the possession of something that you can do whatever you like with. You are in the possession of life already, so go do something with it, make it not just a possession but your own.