I have millions, but here is #1.
Bodybuilding magazines show BB training in peak condition, using fake plates in the most part, I've seen it with my own eyes. They hold this condition for 2-3 weeks a year, the rest of the time they are much smoother.
Now young guys look at these pics, see the guy lifting, very lean, and automatically thinks that lifting, training is where its at.
If the magazines were to print pics of the guys fully dressed and eating 5000-10,000 calories a day, nobody would buy it, boring pics.
So your eyes tell you that to look like them you need to train like them.
Gyms are full of skinny guys doing concentration curls.
In your formative years, gain as much mass as you can by eating vast quantities of food, training hard on the compounds and resting.
Pretty boring pics dont you think