Sonic always addressed his best friend by his nickname and took advantage of his mechanical skills when it suited him. No one thought much of it.

Based on the comics universe. Donald is just a boy, but he believes he's ready to make it on his own. He's through with depending on others. However, when Donald meets a young Mickey Mouse for the first time, he'll discover that it's better having someone be there for you- and what it feels like to be there for someone else.