You can never know the result before taking the action. So, you're not stupid. You're just not such a good fortuneteller. If you would do everything the way it 'should' be done, you would be thoroughly bored. Your 'mistakes' keep you alive, curious and enthusiastic.
All great inventors have high tolerance to 'mistakes'.
Are you expecting to do something 'perfect' the first time. Which means, you already learned something new. On an energetic level, that means you are expanded. Every 'mistake' you make is just a lesson to take you further on the path. Let go of the concept of mistakes, and you could enjoy inspiration speaking through you, while something unexpected pops up as your result.