Writing a Synopsis

What is it about The Dreaded Synopsis that so many writers have a problem with?

I've not had to write one yet, and if I wrote one now I don't think I would be under the same pressure as if I were to write one for an agent/editor when submitting a novel.

I see lots of posts by agents simply stating that we are professional writers, and there shouldn't be a problem writing a synopsis, and yet so many of us have a problem with this.

Thankfully it'll be quite some time before I need to write a synopsis myself and hopefully it will be a breeze. LOL I'm a dreamer!