I don't typically link blog and I do my best to write substantive original material, but the following is too good to pass up.  It's how I feel and how I've approach work in the last year or so.  From Ayende's Reducing The Cost Of Change blog post this morning:

That mindset, at least for me, starts from the first line of code. I treat each piece of the project as utterly disposable. Since I don't really care how each individual piece works, I am able to roughly sketch a fair amount of the application very rapidly, and then focus on each of the items in isolation, and replace that with a much better implementation. I think that I stated before that I tend to rewrite most of my application core at least two or three times before I am happy with them.

When you have disposable pieces, it is no big deal if you mess up and need to start over, because the whole project is structured in a way that allows you to do so. Going back to using my current project as an example, the algorithm used for the core part of the system is crap. I thought it up while being on a coffee break, and it is enough to demonstrate what the software is supposed to be doing. I don't really care, because the moment that I do need the real algorithm, I can drop it in (need to change the implementation of a single method).

I can't improve on that, so I won't try.