Op I'll like to add that, if you buy $100 worth of Bitcoin which is currently 0.0015BTC, and the price start dumping, in real sense it's only the worth of the Bitcoin in dollar or any currency you compare it to that reduces the value of the Bitcoin you bought remains the same. That is, you still have 0.0015BTC in your wallet but the value has reduced. It might dump as low as -50% which means your $100 worth of Bitcoin would be $50 but your Bitcoin figure remains the same, it's only the value that changes.
Is that someone he doesn't know? I don't think so because based on what he has written in his post, he clearly understands how it works and that the value of the Bitcoins bought drops and not the amount of Bitcoins. Even an absolute newbie would understand this thing in my opinion.
Besides, the topic wasn't about this nor was the question asked by OP. He asked about what you would do in case the market goes down and you see your investment losing value and you see no sign of any bullish movements soon. A newbie without ample knowledge about the market would probably panic in such a situation and might sell at a loss. An experienced and seasoned investor or trader would make use of the opportunity and buy more if they have the funds for that.
Dips and corrections are a reason for fear in new investors while they are considered opportunities to gain more profit by old and experienced traders.