This question already has an answer here:
$FB is $180 today.
If it were to lose 50% of it's value it would be worth $90.
If it was to then gain 50% back it would be worth $135.
So the percentage change was the same but the dollar change was different.
I suppose this presumes that bad news affects the percentage drop in the same way that good news affects a percentage gain, if bad news makes the stock drop less (all other things being equal) than 50% here then it might not be the case.
Does this mean that losing in the stock market is far more destructive to your portfolio than winning and that you should not lose at all costs?