The seed of a tree contains the idea of the adult but does not fully realize the form and potency of the adult. The embryo grows. It becomes larger. It looks more like the adult and has more of the uses. Eventually it bears fruit. Later, it dies and its body feeds other organisms.
We have the luxury of treating software like that. A bridge is not like that; there is never a baby bridge, but merely an unfinished bridge. Bridges are a lot simpler than software.
It is good to think of software as growing, because it allows us to make useful progress before we have a perfect mental image. We can get feedback from users and use that to correct the growth. Pruning off weak limbs is healthful.
The programmer must design a finished system that can be delivered and used. But the advanced programmer must do more. You must design a growth path that ends in the finished system. It is your job to take a germ of an idea and build a path that takes it as smoothly as possible into a useful artefact.
To do this, you must visualize the end result and communicate it in a way that the engineering team can get excited about. But you must also communicate to them a path that goes from wherever they are now to where they want to be with no large leaps. The tree must stay alive the whole time; it cannot be dead at one point and resurrected later.
This approach is captured in spiral development. Milestones that are never too far apart are used to mark progress along the path. In the ultra-competitive environment of business, it is best if the milestones can be released and make money as early as possible, even if they are far away from a well-designed endpoint. One of the programmer's jobs is to balance the immediate pay-off against future pay-off by wisely choosing a growth path expressed in milestones.
The advanced programmer has the triple responsibility of growing software, teams, and persons.
A reader, Rob Hafernik, sent in this comment on this section that I can do no better than to quote in full:
I think you under-emphasize the importance here. It's not just systems, but algorithms, user interfaces, data models, and so on. It's absolutely vital as you work on a large system to have measurable progress toward intermediate goals. Nothing is as bad as the special horror of getting down to the end and discovering that the whole thing just isn't going to work (look at the recent debacle of the Voter News System). I would even go further and state it as a law of nature: no large, complex system can be implemented from scratch, it can only be evolved from a simple system to a complex system in a series of intentional steps.
To which one can only reply Fiat lux!