If you're really looking to make yourself miserable, tell yourself you can paint the whole house in a weekend.
Think about it this way: You probably wouldn't trust a contractor who bid you a two-day paint job, unless there are six of them working at a time. That's because they should offer a wash, any repairs you have to make (which might involve sanding or priming) and a couple coats of paint. In other words, professionals would estimate at least three or four days for three painters on an average-sized house [source: Tedeschi]. If it's just you and a friend? Give yourself at least a week to do all the same steps, and don't be shocked if it creeps into two.
We all know the most pressing issue with underestimating your timeline: an annoyed spouse who no longer wants to spend "just one more" summer night up a ladder. But beware: If you don't plan out far enough, you might find yourself in the midst of a forecast that's far stormier than a ticked-off partner.