A lot of it is fundamentally physics - Minis weigh about half as much as a lot of "modern" cars.
That means it takes less effort to accelerate them, be it...
forwards - when you press the go pedal;
backwards - by wind resistance because it uses a bigger proportion of your power as the speed increases than it would for heftier car;
sideways - when you turn your steering to go round a corner;
upwards - when you hit bump in the road.
If you're unlucky enough to have one of those modern chunksters to run in to you, even if your Mini is tough enough to ride the blows, you'll be doing more harmful rapid deceleration inside it by virtue of that same ability to change direction 'n speed better.