Some people have asked me why the Lord Ruler was so careful to keep secrets about Allomancy. What would it have mattered if he let out that there were atium Mistings?
Some of the secrets offered a sizable tactical advantage. Keeping back duralumin and aluminum gave him and his Inquisitors (the only ones told about those metals, other than a few select obligators) tools that nobody knew about. Very few Inquisitors could burn duralumin (and most who did it gained the ability through the use of spikes reused from previous, dead Inquisitors—and those spikes were therefore much weaker.). However, those who did have the power could appear inordinately skilled in Allomancy, enhancing the Lord Ruler’s divine reputation.
Beyond that, knowledge is power. I believe that. And I think that if you’re the Lord Ruler, you want to keep a few secrets about your magic system. Mistborn are very rare. Mistings among the nobility—particularly in the early centuries—were not rare. If they’d known about atium Mistings, it could have upset the balance by creating too many superwarriors.
Plus, if there are unknown superwarriors to be had, then you want to keep them for yourself.
Yomen Is a Seer
That raises the question of how Yomen discovered that he was a Seer. He mentions that atium was too valuable to waste on testing for atium Mistings. That’s true, but incomplete. The Lord Ruler did test his obligators for the power, particularly the high-ranking ones. Those he found were told of their power and used as an extra level of security. There weren’t many, but there were some—and they tended to rise very quickly in the ranks (like Yomen) and be given important positions. Yomen’s power with atium made him a valuable secret weapon, and when in a position of power, he could use his ability to quell rebels or perform feats of wonder to keep the people in line.