It's not that he's incompetent or can't get it done. It's not that at all. What happens is that after he departs to do the task (fetch something from the store, run an errand), he will decide that what you told him is not what you really wanted. He will decide that, since he's a problem solver, he will get you what you really wanted. What you would have wanted if you'd known it was available. Something better than what you asked for. Perhaps you had subconscious desires that you failed to communicate. Perhaps instead of Tide, you really wanted Cheer. It's on sale, and you like a sale, right? Perhaps instead of depositing to checking, you'd like it in savings. You do need to save, after all. What a great man he will be when he returns, victorious, with the thing you didn't even know you wanted. Men are problem solvers.

I have learned to be very specific with my wishes when sending a man (any man) to fetch me something specific that I want. I explain the size, the brand, price doesn't matter. If they don't have that brand and size, please don't buy me something else. This is all I want.
Alas, today I forgot. I am having bacon and inferior bagels for brunch.