The Kohn-Sham (KS) equations are relatively simple to solve without incorporating the exchange-correlation function, but this approach results in a significant loss of information. We do know exactly what is missing: the precise exchange and correlation. However, the method to retrieve this information is not straightforward. Jacob’s ladder offers a step-by-step guide, breaking down the development of Density Functional Theory (DFT) into smaller, more manageable parts. Each step brings us closer to achieving the exact function.