Spreadsheets are anarchy` because they allow users to freely input data without any restrictions, which can lead to inconsistencies and errors. To combat this, Google Sheets offers a feature called `data validation`, which enables users to add rules to specific cells or columns, ensuring that only relevant information is entered. Data validation allows users to limit the types of input allowed, such as dates or numbers, and even provides dropdown options for easier selection. Additionally, data validation can be used to enforce scoring systems, like pet attributes, and reject invalid inputs. The author demonstrates how to use data validation in Google Sheets by creating a dropdown menu for pet types and enforcing a scoring system. They also touch on conditional formatting, which is separate from data validation but works well with it. Overall, data validation makes Google Sheets a powerful tool that can be used to build custom tools and automate workflows without the need for external software.