What is meant by the idiom Have a bee in your bonnet?

To be obsessed with a particular idea or notion, especially one that is eccentric or impractical.

When a bee is in your bonnet, it’s buzzing around in there and distracting you from everything else. In the same way, when you have a bee in your bonnet, you can’t stop thinking about that one idea. It’s all you can think about, and it’s preventing you from focusing on anything else.

The phrase "have a bee in your bonnet" is thought to have originated in the 17th century. It was originally used to describe someone who was behaving strangely because they were possessed by a bee. Over time, the meaning of the phrase changed to refer to someone who was simply obsessed with a particular idea.