As everyone has undoubtedly guessed. Hu-cards are very fragile, unlike an NES cart where you could bounce it off a wall, and more than likely get it to work. That kind of shock could wipe a Hu-card. As could someone sending them through the mail without proper protection.
It is funny that black section of the card is what holds the game information. The rest is just eye candy. So if anything happens to it..... I would avoid putting unnecessary pressure on that part of the card.
Note this also applies to Master System cards, obviously.
So, be gentile