If you have a grasp on distance rather than speed, you could figure out how quickly that speed would get you across that distance, assuming straight-line travel.
Let’s say I live 10km from a relative (about 6 miles) and I know it takes them about 20 minutes to get here when the road’s clear, that means I know they’re doing about 30km/h (18.6mph) on average to get here. Pretty standard for urban driving. At an average speed of 300km/h that journey would take 2 minutes.
Equivalently, a 2 minute journey now takes 12 seconds. This ignores the fact that there’d have to be one heck of an acceleration and deceleration at either end to get that average, but nonetheless, 300km/h is scary speed.
Or to put it another way, one accidental twitch of the steering wheel at that sort of speed and even the best downforce in the world isn’t going to stop you turning into a break-neck, sideways, tumbling disaster.
You could watch car disaster videos online if that helps. Or if you don’t like the idea of potentially watching people die, seek out people playing sandbox games like BeamNG where they set up horrifying scenarios, but no-one gets hurt.
Flag Admiral Stabby earned that knife.