The game's data can get corrupted for many reasons and in many ways.
Steam is a digital distribution platform which distributes thousands of games to millions of users. Steam provides a user with automatic updating of games, installation, community features and purchasing options.
o Select "Verify Integrity Of Game Cache" o Once this process is finished click Ok/Done. For more information regarding mods, please visit the “How to verify you have no mods and uninstall them” FAQ.
One of them being when Steam prompts an error after you validate Steam files and the file doesn’t get reacquired.