According to the Midrash (Ecclesiastes Rabba 1:13), we should thank God for creating us with the attribute of forgetfulness, for as a result we can learn things more than once.
If we were unable to forget, then whenever we would study some subject a second time, the experience would be identical to the first time.
Now, thanks to forgetfulness, our learning always contains an aspect of renewal.
Nevertheless, sometimes it is easier to learn three new pages than to review one page, for in new things there is power and rejuvenation.
The process of review, of relearning old ideas – fascinating as they may be – will inevitably be deficient simply because it is not new.
–Rabbi Adin Steinsaltz