Diamond in the rough
When a diamond is found, usually in a mine, it isn't the sparkling thing you see in beautiful jewellery. It's rough and may be half-covered in other substances. It takes skilled cutters and polishers several months to create the gemstone that will eventually be sold. The cutter will study the stone from every angle to decide how they can obtain the maximum reflection and effect. So 'a diamond in the rough' is something that does not look much at the moment but has the potential to be something of great value one day.
The first draft of a story that could be a best-seller after all the problems have been sorted out might be referred to as a 'diamond in the rough'. More frequently, however, the idiom is used to describe people. In a film, there may be a cool character who seems to have all the advantages but a poorly mannered, badly dressed person turns out to be a much nicer, braver person. This sort of character is a 'rough diamond'. The green monster in the movie Shrek is a good example.
Slightly different is a good-hearted person on the edge of the criminal world. They help the innocent and show their good qualities. They, too, are 'diamonds in the rough'.
Hold your horses
Do you ever watch cowboy movies or westerns as they are often called? They aren't as popular as they used to be and some of the films showing Native Americans as savage enemies are definitely not acceptable in these modern times. But there are plenty of good westerns and a look in the video store might be worthwhile. They contain cowboys, great herds of cattle, lawless towns with saloons, sheriffs, marshalls, gunfights and, of course, horses.