You are smaller than the average for all species. As a small individual you are not as well equipped to resist poisons, injuries and alcohol. You use the trait every time your diminutive size might be a factor. This trait reduces your encumbrance limit by 1kg per step of the trait. If you have -2, your encumbrance limit is 10 kg instead of 12 kg. For every level of this trait, you are half a foot shorter than average. A character with Big cannot take Small without first getting rid of Big.