Why this matters
Every extra instance variable beyond two is a sign of a hidden concept waiting to become its own class. A class with seven fields like firstName, lastName, street, city, country, email, and phone is really four concepts — Name, Address, Location, and Contact — jammed into one. Decomposing them reveals the domain structure and dramatically increases cohesion: every method in a two-variable class uses both variables, which is the definition of maximum cohesion.
Code Challenge
Study the messy code, try to refactor it, then reveal the clean version.
Key takeaway
Every extra instance variable beyond two is a hidden concept waiting to become its own class. Decompose until each class has at most two fields — the resulting hierarchy will reveal the true structure of your domain.