Pretty Good

There once was a pretty good student, Who sat in a pretty good class.
And was taught by a pretty good teacher, Who always let pretty good pass.
He wasn't terrific at reading, He wasn't a whiz-bang at math,
But for him, education was leading, Straight down a pretty good path.
He didn't find school too exciting, But he wanted to do pretty well,
And he did have some trouble with writing, Since nobody taught him to spell.
When doing arithmetic problems, Pretty good was regarded as fine.
5+5 needn't always add up to be 10, A pretty good answer was 9.
The pretty good class that he sat in, Was part of a pretty good school,
And the student was not an exception; On the contrary, he was the rule.
The pretty good school that he went to, Was there in a pretty good town,
And nobody there seemed to notice, He could not tell a verb from a noun.
The pretty good student in fact was, Part of a pretty good mob,
And the first time he knew what he lacked was, When he looked for a pretty good job.
It was then, when he sought a position, He discovered that life could be tough.
And he soon had a sneaking suspicion, Pretty good might not be good enough.
The pretty good town in our story, Was part of a pretty good state
Which had pretty good aspiration, And prayed for a pretty good fate.
There once was a pretty good nation, Pretty proud of the greatness it had,
Which learned much too late, If you want to be great, Pretty good is, in fact, pretty bad!
My question is: How can anything be pretty anything? Pretty is an adjective, meaning nice, acceptable. Good is another adjective, meaning OK. Things are either good, better or best and if they are not, they are not pretty. However I do get it, we need to better than "pretty good" in life......we need to be Real Good!