Did we test enough?

Often you will say to your self or asked by your project manager: "Did we test enough?"
Sorry for this, I won't give you the answer on this question. As there are much better articles and books explaining when to stop. Instead I will give you a similar question(s). Hoping to trigger you to find the answer for your self.

Imagine that testing can be seen as reading books. And you have books on several topics and genres. You have also multiple writers on the same topic. When will you stop reading? When do you have enough knowledge for the next step?

When you reader start learning to read you picket those magic books with colored pictures. After a while you learned how to recognize some words. Here your journey of reading started. During your travel you learned more words and you might become interested in reading. After a while you figured out that reading more made you learn more, on college, university or your own free time.

You build your own reference of books and on certain genres you professionalized on an acceptable level. Did this stop you reading books on that genre? If you are interested then you keep on reading. If not, you stop reading that book, perhaps after reading just a view pages. Or you continue with another genre.

Perhaps the similarity with testing is asking your self: "Am I still interested to continue reading?"
In testing you also start with those funny screens. After a while you recognize certain defects in a system. You discovered that there is a certain grammar in testing to help you testing much better. You start using techniques. After discovering the process of testing in a certain way. you will notice that there are also other ways. Other genres for example Agile testing.

Related to the initial question: "Did we test enough?" Are you able to say you "read" enough?

For me testing is the same. I love reading and after a certain period I discover new writers and new genres. And both I hope to do for a much longer period.