Everything starts with "Hello world!".
Incidentally, regarding the previous sentence, I have a problem with the grammatical rule that punctuation should fall within the bounds of the quote marks, should a quote complete a sentence. That's why I included a full-stop after the quote.
In my mind, the exclamation mark is capping the sentence "Hello world!", and the full-stop is capping the entire sentence. The 'official' way to end the sentence would create ambiguity. Am I exclaiming that "Everything starts with 'Hello world'", or am I simply stating that "Everything starts with 'Hello world!'"?
Even that question mark would make things weird if it had to be inside the quotes. I'd read that as quoting a question, not asking one...
It's just something that bugs me sometimes.