You've got to know where the line is if you are to keep from crossing it.
In snow/ice, I test the conditions periodically to see what level of traction I have. Not all snow/ice behaves the same, and traction can vary drastically. In a safe place, I will mash the brakes to see what my stopping distance is. Then I will swerve a little to see cornering performance.
A common natural reaction people have in panic situations is to mash the brakes and steer away from the threat. Often times the best thing to do is ease off the brakes and gently steer around the obstacle. The wheels can only steer the vehicle if they are turning. Locked wheels are no longer steering, and turn the car into a sled. Getting into a panic and steering more sharply will reduce the ability of the vehicle to manuver around the object. Very slight steering off the direction of slide will give maximum traction to changing course.
Some of these crashes could have been avoided by gentle steering rather than locking up the brakes.
Watch at 6:40 how this car instantly steers just after the driver releases the brakes. Allowing the wheels to turn restored cornering traction.