What does Bilbo accomplish that makes him feel bolder?

Bilbo feels bolder after killing the giant spider.

"Somehow the killing of this giant spider, all alone by himself in the dark . . . made a great difference to Mr. Baggins. He felt a different person, and much fiercer and bolder in spite of an empty stomach, as he wiped his sword on the grass and put it back into its sheath. ‘I will give you a name,’ he said to it, ‘and I shall call you Sting.’ ”