This morning I picked up trash as my puppy Yoda swam after his ball at a nearby spring-fed pond. To my constant surprise, I kept finding “new” trash in areas I already went through with a watchful eye. Sometimes it took 10-15 passes through the same area from different angles to find all of the trash.

Big items like dirty diapers stood out. (Yes, there were two of them — don’t worry, I wore doggy bags on my hands.) Smaller items like cigarette butts and bottle caps kept surprising me. One or two small bits of trash don’t ruin a place but the combination of many that tend to drag down an otherwise beautiful spot in a kind of subliminal, unexplainable way. Before heading out, I walked around the trash-free corner of the pond and it felt so much better.

It dawned on me that I’ve experienced this feeling before when working on NanaGram. So often I’ve tested something, thinking I’m done, only to test once more and find multiple new issues. This is especially true when it comes to testing with users.

Taking one pass (or even a couple) through something, telling yourself you’ve done the job and moving onto the next thing isn’t the way. It takes multiple passes, often tens or hundreds — from different angles and perspectives, sometimes over time — to really get to the bottom and make something great. You might even have to deal with a dirty diaper or two.