In typical 37signals fashion, the wisdom in these pages is edgy yet

Why are you doing this? Ever find yourself working on something
without knowing exactly why? Someone just told you to do it. It's pretty
common, actually. That's why it's important to ask why you'reworking
on______. What is this for? Who benefits? What's the motivation behind
it? Knowing the answers to these questions will help you better
understand the work itself.
What problem are you solving? What's the problem? Are customers
confused? Are you confused? Is something not clear enough? Was
something not possible before that should be possible now? Sometimes
when you ask these questions, you'll find you're solving an imaginary
problem. That's when it's time to stop and reevaluate what the hell you're
doing.
Is this actually useful? Are you making something useful or just
making something? It's easy to confuse enthusiasm with usefulness.
Sometimes it's fine to play a bit and build something cool. But
eventually you've got to stop and ask yourself if it's useful, too. Cool
wears off. Useful never does.
Are you adding value? Adding something is easy; adding value is hard.
Is this thing you're working on actually making your product more
valuable for customers? Can they get more out of it than they did
before? Sometimes things you think are adding value actually subtract
from it. Too much ketchup can ruin the fries. Value is about balance.

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Will this change behavior? Is what you're working on really going to
change anything? Don't add something unless it has a real impact on
how people use your product.
Is there an easier way? Whenever you're working on something, ask,
"Is there an easier way?" You'll often find this easy way is more than
good enough for now. Problems are usually pretty simple. We just
imagine that they require hard solutions.