Question

why did tom feel discouraged? ​

Answer 1

You didn’t post any paragraph or from where is this line taken
Then how could we answer

Answer 2

Answer:

Thirty yards of board fence nine feet

high! Singing, he dipped his brush; passed it along the topmost plank ; repeated the operation ;

did it again ; compared the small whitewashed space with the vast area of Aunt Polly's unwhite -

washed fence, and sat down discouraged.