Consider the following qualification rules for different Obamacare plans.

If income < 20k then Plan-1

If income >= 20k and < 50k then Plan-2

If income < 30 k and net worth > 150 k and single then Plan-2

But what about this applicant?

Client: unemployed, single, net worth > 150 k and income < 20 k

Since income is < 50 k the client qualifies for Plan-1 or Plan-2. Since income < 20 k client qualifies for Plan-1. Since net worth > 150k and single and unemployed the client qualifies for Plan-2. The computer system will then freeze - probably from stack overflow.

In actuality the qualification rules for various different plans are much more complex than the example above and inconsistency is very hard to track -especially when rules refer to other rules ("as per", "subject to", "as qualified by") as is standard fare for legalese. Moreover, several different programmers will be coding different sections of the rules. And the blame lies then with whom?