How do you respond when someone tries to improve your idea/plan?

How do you respond when someone tries to improve your idea/plan?

Sometimes people are helpful, but sometimes they are not. It drives me crazy when I have an idea and someone "improves" on it only to make my idea resemble something else. Say you invent a fast car and a person pulls the wheels off to build a tricycle thinking they somehow made your idea better? How do you respond... when it's your SO?

Maybe you plan a relaxing day trip and the person adds a dozen errands to the trip. What then?

How do you respond when someone tries to improve your idea/plan?
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