1.2.2.3. 💡 First Principle: Test the Theory to Determine Cause

💡 First Principle: Systematically testing your hypothesis by changing one variable at a time is the only way to confirm or deny it, turning a probable cause into a determined cause.

Scenario: Your theory is that a faulty RAM module is causing the boot failure. To test this, you power down the PC, open the case using proper ESD precautions, and reseat the RAM. If that fails, your next test is to swap the RAM with a known-good module.

Once you have a theory, you must test it to see if it's correct. This step is about isolating the variable and confirming the root cause.

Key Actions:

• One Change at a Time: When testing, change only one thing at a time. If you change multiple things and the problem is fixed, you won't know which change was the solution.
• Confirm the Theory: If your test resolves the issue, you have likely found the cause. For example, if reseating the RAM fixes the boot issue, your theory was correct.
• Deny the Theory: If your test does not resolve the issue, your theory was incorrect. You must then form a new theory and test it. For example, if a known-good RAM module doesn't fix the issue, you might form a new theory about the video card.
• Escalate if Necessary: If you are unable to determine the cause after testing several theories, it may be time to escalate the issue to a senior technician or a different team.

⚠️ Common Pitfall: Not having a "known-good" part for testing. Swapping a potentially bad component with another potentially bad component doesn't prove anything.

Key Trade-Offs:

• Destructive vs. Non-Destructive Testing: Always perform non-destructive tests (like checking a setting) before performing destructive tests (like reinstalling an OS).

Reflection Question: Why is the principle of "one change at a time" so critical during the testing phase of troubleshooting?