Congress enacted two statutory exceptions to the general 3 year rule upon proof by IRS. This fact bears repeating.

FORBES: IRS Lacks Statutory Authority to Extend Time to Assess Tax

One basic rule for limit-making is that the burden of proof should fall on those who want change especially since the changers often want to keep on changing indefinitely: cutting the abortion limit by a fortnight was, for some, merely an interim goal on the way to a tighter squeeze or an outright ban.

ECONOMIST: Bagehot

The exception to that rule is online gambling, where companies are required to have proof someone's age before allowing them to bet.

BBC: Tackling under-age online sales

As a rule of thumb, products that speak to basic needs are more recession proof.

FORBES: Is Your Marketing Ready for a Double Dip?

The best proof is that we now look back at both the Civil Rights Act of 1964 and the filibuster rule change of 1975 and wonder that they once seemed so impossible.

NPR: In Filibuster Fight, Both Parties Switch Stances