Originally Posted by bluntpencil
Actually, it depends on the planet in the Imperium. Large swathes of the Imperium have feudal nobility, others have slave classes (lol mutants) who cannot advance at all. Many planets will have you born into a job, regardless of your genetics. On an Agri-World you will be a farmer. That is all. On Cadia, you will be a Guardsman. That is all. Those that aren't are unusual.
The Tau cannot leave their Caste, but can advance within their Caste. An Earth Caste can become a professor, a Fire Caste a General, an Air Caste an Admiral, a Water Caste a Foreign Minister...
Okay, the Ethereals are in charge, but there is more mobility here than in the Imperium.
The difference is, the Guardsman can dream of one day, somehow, getting leave to go home and open a shop. The Agri-world farmer can daydream about his alternate life as the chapter-master of the Blood Angels, saving the universe in the name of the god-emperor but the Tau Fire-Caste is not even free to imagine a world where he is anything other than a fire-caste warrior. There is only that and nothing else.
Disclaimer; May not actually be the case. Canon may vary, please consult your physician before proceeding.