That's the fundamental problem. It's pretty unlikely you really know what too fast is, but you think it's too fast. First, stay off the brakes. Second stay steady on the gas or accelerate very slightly. The only way you know for sure you are going too fast is if the front or rear of the car is already sliding. If all four wheels are sliding, then yea, verily you are at the limits, and even then, you stay the course. Upsetting the balance of the car with a throttle change or braking is the worst thing you can do, and guaranteed to send you touring the tulips.
This is all stuff you can play with in a big parking lot on a rainy or snowy day. The wet/snow only makes the car slide easier so you don't have to go as fast to get the same education.
One of the hard lessons about handling difficult situations is it always happens the same way pretty much regardless of speed. If you learn at low speed, the risk of something really bad happening (like rolling the car) is a lot smaller. That's why driving schools put you on a skidpad, wet it down, and have you practice car control at speeds that will not result in extreme danger.
Once you have the recovery techniques down and feel comfortable with the car sliding around, then you can go out onto the dry pavement and practice the same stuff with confidence that you'll be able to do the right thing. The speed will be a lot higher, but the skills you need to retain and regain control have already been polished under controlled conditions so you do the right thing more as a reflex, not as a conscious thought process.
For example, motorcycle road racers have to learn what it feels like to lock up the front wheel under braking. It's the only way to know where the true threshold is, and the only way to learn what to do when it happens. So you practice locking up the front brake at low speeds (15 -20 mph), learn to release the brake, straighten the bars, and grab the brake again in less than 0.7 seconds. If it takes longer than that, you fall down. Guaranteed.
So you learn this skill, and when you accidentally lock the wheel at 90 mph going around some slowpoke going into turn 3 at Sears Point, you already know what to do, it happens with exactly the same timing as it does at 15 mph, and you recover, brake successfully into the turn and drive around slowpoke without incident.
