52. The Rule That Prevents You From Cheating Your Own Model

Series: How Machines Learn: A Complete Guide from Zero to AI Engineer Phase 6: Machine Learning (The Core) You built your first model. You trained it. You tested it on the same data. It got 98% accuracy. You felt great. Then you tried it on real data. It bombed. That moment right there is what this post is about. It happens to almost every beginner and it happens because of one mistake: you let your model peek at the answer key before the exam. What You'll Learn Here Why you can't test a model o