There should be no shame in admitting you made a mistake - I've made several hundred thousand dollars in mistakes - sometimes they turned out to be the same mistake twice - but I owned up to them, and worked harder to make it right.
I've been bit often by:
Poorly Defined Requirements
Incomplete Understanding of the Problem
Incomplete Understanding of the Solution
Customer Created Access Difficulty
Customer created process issues
Poor documentation or data inputs
Excessive Complexity Customization driven by customer needs
I'm getting better with time, and I'm better at determining what the actual requirements are, and I now more fully understand what my solution is capable of too.
Similar to the study a while back of whether VCs would rather fund someone who's a "natural" at what they do or someone who's had to work hard to reach that "natural" level. (It's the former.)
I've been bit often by:
Poorly Defined Requirements
Incomplete Understanding of the Problem
Incomplete Understanding of the Solution
Customer Created Access Difficulty
Customer created process issues
Poor documentation or data inputs
Excessive Complexity Customization driven by customer needs
I'm getting better with time, and I'm better at determining what the actual requirements are, and I now more fully understand what my solution is capable of too.