Chad Callihan has a great analogy for eager spools:
Think of a time when you went to someone for help on a problem. Rather than walk you through how to solve the problem, that someone just groans, speeds through solving it for you, and sends you on your way without any explanation.
Did you learn anything? No.
Will you need help again next time that same problem comes up? You bet.
I also like Erik Darling’s explanation that an eager spool is SQL Server’s passive-aggressive way of telling you that you need an index but no, you’re just too busy to create one so I’ll just keep working here all day and do you even call your poor mother anymore?