In GT5, when your rear wheels lose grip you are almost guaranteed to spin out of the road. In comparison, controlling a real car in that situation seems almost too easy:
I agree with stevetam... it's easy when you're an experienced drifter... and you're initiating those drifts. But if you're not: and I'd wonder whether you'd actually done any high-speed drifting on the racetrack (not the low speed parking-lot stuff), and if it catches you by surprise, it's another thing entirely.
Let's set this clear: There's a big difference between intentionally upsetting a car going into a corner in order to initiate a drift and hitting a bump or getting lock-up under braking and having the car start to fishtail into it.
In the former, you expect the car to break loose, and already have a dab of oppo dialed in when the rear end starts to arc wide, or have it dialed in in your head, only awaiting that tugging at your backside and fingertips to complete the circuit.
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If it happens when you're not pushing the car into it... how easily you can catch it depends on the speed, the tires, the type of car you're driving and the situation in general. If it's a lower speed corner and you still have plenty of front-end grip left and you've got a front-driver or an AWD, you can countersteer (take your time... no rush...

) and mash on the gas and the car will straighten out, easy-peasy. If it's rear-wheel drive, don't mash anything (or lift)... just counter and trust your instincts.
If it's a slight drift due to letting off in a corner, and you're not going too fast (say just 80-100 km/h), no biggie... the steering will (usually) kick-back and nudge you in the right direction... take it easy on the pedals and you're back on line, just two or three meters wide. If you've got a front or four-driver, you can let it drift out further and then catch it on the throttle for kudos points... if you're in a rear-driver, you can tease the throttle to hold the angle longer.
If you recover too slowly, or over-recover, you can have the car fishtailing into the weeds.
If it happens at 160 km/h or over, or the car is well and truly sideways and you don't have the reflexes of Kimi Raikkonen or Jason Plato:
Wrap your arms around your shoulders (don't break your thumbs on the steering wheel, baby) and kiss your behind goodbye.
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I've experienced all of the above... caught some of them... and the last one was well and truly a learning experience. You have a road-car go sideways on you at 160 km/h (100 mph) due to a locked brake, a patch of oil or a bump in the road, and you're at a 90 degeree angle in the blink of an eye. And at a 180 degree angle in two blinks... and at a 270 degree angle in... well... let's just say that while drifting is exhilirating fun... spinning is not.