I learned "by-heart" tables from 2 to 20 when I was 8 because I had no choice.
Since my childhood, I remember hundreds of Hindi poems, even entire books word by word – some because I had no choice, but many because I love them.
My love for Urdu poetry started barely a decade ago. And in that time, I have fallen in love with and memorized hundreds of Urdu poems.
Even though they are used interchangeably, there’s a difference between unforgettable and memorable, in my opinion. The former applies to stuff where there is no particular conscious attempt from the audience. The latter needs some effort, interest and passion.
The aim of a good training session, a speech, an article, an email or a person should be to become memorable (not necessarily unforgettable).