# Any 2 Out Of 3 But Never 3 - Rule

I stumbled upon an interesting concept from our nature.

Some of you may know about the CAP theorem in computer science. Cap theorem states that it is impossible for a distributed data store to simultaneously provide more than two out of the three guarantees. The three guarantees are 1) Consistency, 2) Availability, 3) Partition tolerance. We can only have two out of these three guarantees at the same time.

You may also know the Good/Cheap/Fast axiom. Cheap + fast leads to lower quality. Good + fast leads to higher costs. Again, only two of these can be valid options but never all three at the same time. You cannot get something done fast that is good and cheap.

In marketing similar rule applies. When you segment your users, you usually do it based on 1) Close to needs, 2) Targetability, 3) Identifiability. For example, if you segment your users based on geo/socio-demographics, you will get high Targetability and Identifiability but will not be close to user needs.

This rule is also in Little’s Law and is part of the queueing theory. I’m sure that the “any 2 out of 3 but never 3” rule is part of many axioms, laws, and theories. If you try to solve a specific problem where three attributes have to be simultaneously fulfilled to 100%. Remember the rule “any 2 out of 3 but never 3”. There is no way to fulfill all three attributes to 100%, but partly as a trade-off.