Chris Aitchison posted "You are NOT a Software Engineer!" saying that you're a Software Gardener instead. An engineer knows what his output is supposed to be, a gardener works by gently tending his garden to a hoped-for result. Good writeup.
Do you try to plan your gardens in such detail that you know where each leaf will be positioned before you plant a single seed? Do people expect estimates (or are they promises in your organisation?) on exactly how many flowers will have bloomed in one years time? Do you have a bonus tied to that? Things that would be perfectly reasonable to plan for a skyscraper seem a little ridiculous when you are talking about a garden.
You probably have a good idea of what your garden should look like a week into the future. You might even have a rough idea of the shape you expect it to be in a year from now. But you have no idea of where each branch, leaf, stem and flower will be a year from now, and if you say you do then you’re really only guessing.
If you were building a bridge or a skyscraper and you told me, before you began, that you knew exactly how it would look when it was finished – I would believe you. If you told me that you knew to some insane degree of accuracy how long it would take to get to ‘finished’ – I would believe you again. That’s how Engineers roll. Tell me the same thing about your garden and I’m gonna call bullshit. Tell me you are going to make it grow faster by hiring more gardeners and I’m gonna laugh at you.