Not everyone can be great at everything. Steve Jobs famously was bad at school. It didn’t hold him back. Too often people shift into a defensive mode when thrown a challenge they aren’t comfortable with. They do their best with it but when the result isn’t what was desired they pull out excuses or curse at the wind.
The common theme from here is to learn from the experience and grow. But that doesn’t help when you’re now in trouble for not accomplishing the task at hand. The lesson I’ve learned in my career is to always set expectations up front. Often that assignment was given to you as a challenge to see if you could achieve something that you hadn’t done before. But just as often it’s because the other party didn’t know that you weren’t familiar with it. They gave it to you because they thought it would be simple.
If you don’t set expectations then there is an information gap between yourself and the other party. That gap will be the cause of any disagreement on outcome.