Fruit of Knowledge

Once, Shiva and Parvati were having 'the fruit of knowledge', which both Kartikeya and Ganesha wanted to have!

 So, Lord Shiva threw a challenge to both his sons asking them to take three rounds of the world and come back!

And The one who would return first would get the fruit. 

Kartikeya flew away on his peacock but Ganesha only had the little mouse as his vehicle. So he encircled around his parents and told them that his whole world lies in their feet. Shiva and Parvati were so impressed with their son's answer that they declared Ganesha as the winner and gave him the fruit!