Some people write well but allow themselves to be disabled by a fear of punctuation and grammar.
They know how to prewrite, organize, and revise, but proofreading for punctuation and grammar causes them difficulties. There's no need to fear these conventions of standard written English. In fact, these conventions can help you become a more effective communicator. In other words, over the years good writers have used punctuation in ways that have made their messages especially clear to their readers. Writers have agreed to follow these practices because they have proven to be so effective.