Hmm, I've addressed this in several other threads with context to brakes, camber, and what a sim can help with vs can't when applied to the real world. I've raced a lot of things in the past 20 years starting with MX, then sportbikes, and now cars. Though I'm not a pro, I have participated in Pro-Am events. My "home tracks" are Willow Springs, Laguna Seca, Sears (Infineon raceway), and Thunder Hill. I've also run several laps of the Nurburgring back in 2011 in a Clio Renault RS 200 Cup car.
For an overarching explanation I might compare the difference to watching a nature documentary vs actually going into nature. In a documentary there are always animals and narration and you get an idea what it might be like. When you go into nature for real you wonder where all the animals are and the explanations of your surroundings but you notice things you might not expect like smells, noises, the breeze, weather... But if you stay in nature long enough you start to bond with it, you're senses start telling you things, and you discover things no documentary could cover. Though there is a commonality of feeling that you can notice, the 2 experiences are VERY different...
Many claim fear is the leading difference but thats not the case. Yes, there is more caution but when the adrenaline is pumping you have to control it and that all but nums fear... Amateurs do go on track with fear of damaging the car and having to pay for it, or someone elses car, etc. but the reality is for a true racer fear is completely replaced by intellectual calculating decisions as you are faced with over 1000 decisions a minute... That leaves little time for fear. I might argue those that are afraid really have no business being out there, but those that are consciously aware of the danger but not letting it influence their craft, are being responsible and all drivers should have some degree of self preservation.
At the grandest level is a competition between yourself and the tools you have at your disposal, like you're taming a beast and commanding it to do your will. Much of this drama can't be caught in a sim but going online with a responsible group like SNAIL can simulate the feeling of door to door racing in that there are firm rules about contact (straight out of a real rule book), just like real racing, and that concern sensation in a sim you have about hitting another driver you're trying to pass is very much like real life, it's not so much fear as it is self preservation, and forcing you to observe where they are fast and where they are slow and plan passes well in advance... In sims the leading driver tends to be more courteous about their own skill and yield, not at all the case in real racing. Many drivers survive contact, its part of the experience, and its all part of the cost... Its why there is a 50/50 rule in racing... Your car must look "clean" at 50 feet and/or 50mph...
Another common crossover feeling in the psychology. Most don't appreciate that psychology is as much to do with racing as actually piloting a car... Both a sim driver and real driver will tell you there are times you just ride the tail of the guy in front of you until he makes a mistake, its only a matter of time before that mirror full of car distracts the driver... In racing there is forward thinking and backward thinking... Both need to be managed and balanced.
The leading weakness in sims are tire modeling, no game gets this right because the engineers aren't real racers and try to mimic real world physics without real world conditions that influence them. GT does a respectable job but the reality is games don't model the slip angle and the fluctuating tire pressures and flex anywhere close to realistically. Yes, there is a cliff when exceeding grip but its more to do with weight transfer than tires... Tires are pushed beyond a limit by other factors beyond just giving up. In real racing you feel all this in your butt, a good racer feels each of the 4 tires and percentage of load at all 4 corners and downforce gain and drop off all in their hands, feel, and butt.
There are a few very rare instances that I've gotten my "race face" in sims and got in the zone and exceeded my true sim skills, and the fact that I was able to do that is what keeps me coming back, but it's rare. Sim skill does degrade over time whereas real life racing does not. Every single lap in the real world you improve... It's like Skiing or riding a bike.
So if you have never raced in real life, then use some imagination, go online with real drivers, pretend like your car is your own real car, learn the limits of the car, then how to stretch them (hard to do in a game with so many options), and you'll be exercising a degree of what real drivers do. For more pointed explanations on specifics I would encourage reading some of my post history over the past year. I too would like to hear from the GT academy guys as all racers have different ways to explain common details but I think GTA is partially promotional between sim and reality so I'm not sure how accurate or direct they would be with comparisons.