What is the 4 3 2 1 rule in real estate?

Excuse me, could you elaborate on the 4 3 2 1 rule in real estate? I'm curious to know what this principle entails and how it's applied in the real estate market. Specifically, what are the four, three, two, and one elements that make up this rule? How does it help investors or homeowners make informed decisions? And what are some examples of how this rule has been successfully applied in practice? I'm looking forward to hearing your insights.