The $\frac{80}{20}$ rule in software development states:

The first $20\%$ of a project schedule takes $80\%$ of the project's money.

The first $20\%$ of a project schedule takes $80\%$ of the project's time.

$20\%$ of a project schedule completes $80\%$ of the project's goals.

The first $20\%$ of a project schedule takes $80\%$ of the project's resources.