单一职责原则——何时停止将代码提取到不同的类中

I'm reading "Rails AntiPatterns" at the moment, and one of the first patterns mentioned is the Single Responsibility Principle. At this point I've encountered SRP enough times to realize that it's a fundamental concept for beginners like me to understand, which is why it's so frustrating that it's not clicking yet. I'm reading "Rails AntiPatterns" at the moment,