From the box backside:

Shout it out, count it out – be lucky as a pig in clover!
Pig 10 is a card game that lets you go hog wild. ­Everything revolves about the number 10. The player who hits 10 with his piglet cards fabulously often, wins.

From the rules introduction:

NINE is nothing special. But TEN is awesome. From ELEVEN on, however, it‘s getting really crummy… Whenever you are able to play a card that turns the result in the middle of the table into TEN, all laid-out cards are yours… but it must not be even a tiny bit more – otherwise, only the rascal who had his turn before you gets the pleasure of it.