Just because you have learned things before does not mean that you are done learning.

Lessons I've already learned:
Milk goes bad really fast-- like, after a week.
Bad milk is really gross.
Bad milk makes really bad pudding.
Soy milk doesn't go bad as fast-- like, lasts more than a month.

Lessons I learned yesterday:
If you are patient, soy milk can also go bad.
If you are stupid, you can learn firsthand that bad soy milk is really gross.