This is a classic logic puzzle that hinges on understanding the motivations and character flaws of the individuals involved. Here is a step-by-step breakdown of the reasoning to solve the puzzle.

First, let's establish the facts given in the scenario:

1. The Builder: He is tasked with building a house but is inefficient or unskilled at the job.
2. The Agreement: He hires a friend to help him, creating a "subcontract."
3. The Condition: The builder explicitly tells his friend, "Don't tell anyone about this subcontract."
4. The Betrayal: The friend immediately tells everyone about the secret deal.

The Core Logical Problem

The central question is to explain the friend's action. A simple answer like "the friend is a liar" or "he's bad at keeping secrets" is insufficient for a logic puzzle. Such an explanation describes a character trait but doesn't deduce the reason for the action from the given information. A logical solution must connect the friend's action to the other elements of the puzzle, primarily the builder's own situation.

Step-by-Step Logical Deduction

1. Analyze the Builder's Motivation: The builder is not a good builder. If he were, he wouldn't need a friend's help. However, he is also not openly hiring a professional. Why? The most logical reason is pride or embarrassment. He is too proud to admit his inability to the public, so he resorts to a secretive, informal arrangement with a friend. The "hidden subcontract" is a product of this pride.

2. Analyze the Friend's Perspective: The friend is aware of two critical things:

   • The builder is not skilled enough to build the house properly.
   • The builder's secret plan is therefore doomed to fail. The house will be of poor quality, and the builder will ultimately fail.

3. Identify the Underlying Problem: The friend recognizes that the builder's biggest obstacle is not just his lack of skill, but his pride. The builder's pride is preventing him from taking the correct and necessary action: hiring a qualified, professional contractor publicly.

4. The Friend's "Tough Love" Strategy: The friend concludes that the builder's pride must be broken for the builder to succeed. The secret plan is an enabler of the builder's flawed pride. To force the builder to make the right decision, the friend must make the secret plan impossible to continue. He must create a situation where the builder has no choice but to abandon his pride and seek proper help.

5. The Logic of the Betrayal: By telling everyone about the secret deal, the friend orchestrates a public failure. The builder's private shame is now public knowledge. This immense social pressure and public embarrassment make it impossible for the builder to continue with his original plan. The only way for the builder to salvage his reputation is to publicly admit his mistake and hire a professional contractor to finish the job correctly.

Conclusion

The friend told everyone about the secret deal not out of malice or simple dishonesty, but as a calculated and drastic act of "tough love."

His betrayal was a means to an end. The end was to force the builder to overcome his pride and get the professional help he desperately needed. The friend, by shaming the builder into a corner, ultimately compelled him to make the correct decision and ensure the house was built properly.