There is no point to explain to him anything, bitcoin price will not go back to 400 dollars, but even if it does it will bounce back and if he leave now he will miss all that for sure. That can't happen, but this guy made us think what if something like that happen and to create some theories.
Price fluctuate all the time, last drop is caused by the sell of in Asia, market lost almost 100 billion dollars in seven days, some alts dropped even more then bitcoin.