Oren wrote today, There is no such thing as a single developer project.  At first this sounds like an obviously false statement, but read on:

There are always at least two people in any software project:

• The developer who wrote the code.
• The developer who read the code.

They are never the same person, even if just by temporal dissonance.

This is a very clever thing to point out, and worth remembering when you're tempted to take shortcuts using the excuse "I'm the only one working on this code so I can wing it."  Who you are today is not who you were yesterday, nor will you be the same person tomorrow.  Write your code with the knowledge that someone else is going to have to maintain it, even if that someone else is you with a bit more experience (and probably a bit of lost knowledge about the details of what you're working on right at this moment).