Jackass is not widely known for his mental acumen, in fact somewhere along the line his name became synonymous with 'idiot' as in the famous quotes below.
“Every woman should have four pets in her life. A mink in her closet, a jaguar in her garage, a tiger in her bed, and a jackass who pays for everything.” Paris Hylton
"Any jackass can kick down a barn, but it takes a good carpenter to build one” Sam Rayburn
But as Mark Twain suggests, poor Jackass has been maligned; “Concerning the difference between man and the jackass: some observers hold that there isn't any. But this wrongs the jackass.”
Now take this astute observation by Jackass; "de worl no level". Jackass is simplifying the Orwellian remark that "all men are created, equal but some are more equal than others". As far as Jackass can see, disadvantage and privilege are both as much part of life as hill and gully are part of the natural terrain here in Jamaica.
We use this expression when we come across unfairness, depending on the context we might also say "Puss and dog nuh have the same luck".