Not every zip-based format behaves like this, Microsoft's zip based container formats tend to require a proper beginning too. For example if you add docx (which

Not every zip-based format behaves like this, Microsoft's zip based container formats tend to require a proper beginning too. For example if you add docx (which is a zip file) to the end of something else and open it in Microsoft Word, it will complain that the file is corrupted, and will suggest to repair it.