In Magento, plugins (Interceptors) can only intercept public methods. This is because the plugin system relies on Magento's object manager to dynamically create proxy classes that can intercept method calls. Since private and final methods are not accessible from outside the class they are defined in, and static methods are not called on an object instance, these method types cannot be intercepted. This mechanism allows for the extension and customization of Magento's core behavior in a transparent and non-intrusive manner​​.