Mastery is a Talent that can be bought for any Skill you have at +30 level, further enhancing it's usage.
It's Aptitudes are Intelligence and Knowledge. This means it's much easier to be a master of lore and logic than it is to be a master of Stealth, or Interrogation, or whatever else you can think of.
Frankly, I see no reason for this being handled that particular way. Wouldn't it be better if the Talent was a special case and always shared Aptitudes with the Skill for which it is bought? As in, Mastery (Dodge) would have Aptitudes of Agi and Defense, while Mastery (Intimidation) would have Aptitudes of Strength and Social, and so forth.