In the wonderful film Pursuit of Happyness,

Will Smith’s character (Christopher Gardner) said to
his son ..

“Hey. Don't ever let somebody tell you... You
can't do something. Not even me. All right?

You got a dream... You gotta protect it. People
can't do somethin' themselves, they wanna tell
you you can't do it. If you want somethin', go
get it. Period.”