Can everyone be a target audience?
You can't target everyone, but you can sell to everyone. Your target market should be based on research, not a gut feeling. You need to go after the people who really want to buy from you, even if they're not the customers you originally set out to reach.
What happens if there is no target audience?
Your marketing messages will be flat and uninspired
If you don't know who that target audience is, you can't use the language or address the pain points that mean the most to them. Your email marketing, website content, and ad campaigns will all be less effective when you don't know your ideal audience.