Shifting Lanes Destroys Your Driivng Ability

You're driving in one lane, the lane shifts but you're still driving in one lane and now you've nearly lost control of your car.  Why?  What is the difference between driving in one lane and driving in one lane?  In my mind, there is none.  Driving on an Interstate today, four lanes, two in each direction, the two lanes shifted slightly to the left.  As soon as the car ahead, that was in the left lane, shifted, the driver couldn't keep his car in his lane.  He veered quickly and violently half-way into the right lane, overly corrected to the left, slightly crossed the white lines again and finally was able to settle down into his lane and continued.  What if he was in the right lane and after shifting left, again shifted to the right?  He would have crashed into the Jersey barriers.  If a car had been abreast of him in the right lane he would have sent that car crashing into the Jersey barriers.  The lanes before, during and after the shifting were exactly the same in road surface, condition, width, and weather.  If shifting lanes are a problem for you I suggest that you take your foot off of the accelerator a comfortable distance before the shift, allow the car to slow down a little, go into the shift, settle down into the lane, then accelerate back to your prior (highway) speed.