Break in doesn't mean drive like a snail. Just drive like casual weekend driver. Don't purposely slam on the pedal. You can still do 120kmh, what matter is it take how long to reach 120 from 0.

Old skol logic is, when engine newly fitted, there's micron difference on each cylinder that cramp up with piston ring. In order to fit in piston, the ring will have to be compressed, after fit in it will expand and hold on the engine block with minimal tolerance. Every combustion cycle, these piston rings will grind through the block inner bore(when piston going up & down). Your dad will ask you to drive 80 bcoz he think you drive too fast. This is a good chance to scare you and put a speed limit on your head. Your SA ask you to drive 80, so you won't complain drink fuel like water! New car so tight, sure will gazzle more fuel geh. If sumore drive like a muoron, sure can go 30cent/km.

Therefore, pushing too much on a newly assembled engine can greatly increased wear & tear. Break in period is a grind in process. Drive below 80 meaning you're shaping your engine to drive below 80 in future! When you shape your engine, you shape it into what you want it to be. Like when you crafting a wooden goose, you don't use a saw to craft although its fast(slam on full throttle to get to 120kmh), instead you'll be using a crafting tool to slowly grind the edge to achieve smooth and curvy surface(gradually increase speed to 120kmh instead).

Hope this explain well.