Oh I just realised the truth of what you are saying. It has been in front of me all along but because I rarely go on my facebook account, I didn't take note.
I love wristwatches and recently I saw a lovely sports watch with a friend. So I went on Jumia, an online retail site, based I think in my country, and browsed through their catalogues. I didn't pick a particular watch, I just checked prices and specifics about the different one that caught my fancy.
Some few days later, they started advertising wristwatches on my facebook account. I didn't take note of it at all but now that I think on it, that sucks.