My favorite book on product development and startups is Getting Real, published in 2006 by the folks at 37signals (now Basecamp).  If you haven't read it (it's freely available online), it's essentially a precursor to The Lean Startup (2011). Back when I was leading a team and running product and OpenPlans, it was like my bible. The copy we had at the office was tattered and torn. One of my favorite ideas / chapters from the book is: "Half, Not Half-Assed".  It's short, so I'll just include the whole thing here:

Build half a product, not a half-ass product Beware of the "everything but the kitchen sink" approach to web app development. Throw in every decent idea that comes along and you'll just wind up with a half-assed version of your product. What you really want to do is build half a product that kicks ass. Stick to what's truly essential. Good ideas can be tabled. Take whatever you think your product should be and cut it in half. Pare features down until you're left with only the most essential ones. Then do it again. With Basecamp, we started with just the messages section. We knew that was the heart of the app so we ignored milestones, to-do lists, and other items for the time being. That let us base future decisions on real world usage instead of hunches. Start off with a lean, smart app and let it gain traction. Then you can start to add to the solid foundation you've built.

This is so important and also so hard to do.  Despite having appreciated this idea since 2006, and having told it to others countless times, I still have not mastered it, and still find myself falling in love with features and ideas that really just end up diluting my efforts. I've been thinking about this because last week I had this exact advice delivered to me on two separate occasions, regarding two things we're building at USV; once from Brittany and once from Fred.  In both cases they were right, and the advice was important and helpful. So, there it is. Nearly 9 years later, still important and still helpful, still cleverly-titled :-)