Lease favorite: creating something that misses the mark. Especially when implementing a feature that isn't exactly what the customer wanted. Unfortunately, customers (and people in general) often don't know exactly what they want until they see it in action. So iteration is more-or-less normal. But I had rather do it once correctly, and I hate that I can't always.
One of the ways I try to ensure less iteration is to sit down with customers and walk through the scenarios to make sure I understand the business aspects of what we are trying to do. So when I'm coding, I can think about what business goals I am trying to accomplish not just the technical ones. I find this aligns the implementation much better to what the customer needs. This helps greatly, but mistakes can still slip through.
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