For me it was that physics was about reality. In high school the key moment occurred when in a physics lab, after calculating and measuring and calculating more

For me it was that physics was about reality. In high school the key moment occurred when in a physics lab, after calculating and measuring and calculating more, we placed a cup on the floor, rolled a marble down the ramp and off the desk - and it landed in the cup! At that moment I realized that all the math I had been studying actually meant something in the real world, and was useful for explaining questions I had about the world.