First-To-File vs. First-To-Use
First-To-File Trademarks
In the United States, the right to use a trademark is based on the rights of the first party to use a mark. Under common law rights this means that if a restaurant opens on one end of the block, another restaurant can't open at the other end and call itself the same name. Allowing that would cause confusion and potentially harm consumers who would have difficulty knowing which restaurant is which. The same holds true for trademarks that are registered. The right to use and exclude others is based not on who is first-to-file, but on who uses it first.
Racing to register a trademark.
First-to-File
This is not the way it is in every country, in fact in most countries a person can lose the right to use a mark in that country merely because they did not register it before someone else - even if they were using it in that country before...