Yes, a startup needs a 'get it DONE' attitude, but that HAS to be tempered with doing things in a maintainable way, and not just duct-taping it together. If you don't, you're forcing a complete rewrite of the entire system, and that is a really dangerous thing to do.
So let's give some better advice for startup programmers:
1) Get it done. Just hack out that code and make it work.
2) Write some tests for the poor thing. If you -can't-, you'll need to do step 3 first and then come back.
3) Refactor/Rewrite that horrid, horrid code you wrote in step 1. Make it readable, first of all. Then make it intelligible. Then make it pretty.
If you work at that company in the future, you'll thank yourself. If you don't, the owners and your predecessors will thank you.
And best of all: Writing good code is a habit. Once you get into the habit, it will horrify you if you ever have to stop, even temporarily.