I don’t know why, but I can’t start building an application until I have the icon. It’s stupid, really; like being unable to start a painting until you’ve signed the canvas, or unable to record an album until you’ve designed the cover art.
Nevertheless, that’s the way it is. I need at least a pretty good 32×32 pixel image which represents what the application is going to be, before I can start to build it. It’s usually a metaphorical representation, not a literal one; I’m not a big fan of the current trend towards photorealistic icons that show real objects as substitutes for virtual ones.
Often the final icon on the delivered application is different from the initial one. At some point the iconic, metaphorical idea from my subconscious will no longer represent the actual thing.