。
The law isn't always fair.
Literal
Law [subject-が] always fair-[assertion-である] [quotative-とは] not-limited
The pattern ~とは限らない means 'it's not necessarily the case that X', 'X is not always true'. It nests a fact with quotative と + focus は, then negates the universality with 限らない ('is not limited to'). Useful for hedged generalizations.