The good part about bitcoin going up and the altcoins going down is that the price of altcoins in dollar value doesn't devalue that much even tho the bitcoin price going down and whatever happens in the end the price of those crypto currencies goes back to what it was on bitcoin price which means the dollar value goes back up as well.
Hence, if you wait for a bitcoin price increase and watch the altcoins going down you can purchase one of the ones you like and than you can purchase that altcoin and watch it go back to its bitcoin value once again and also increase highly on the dollar value since bitcoin worth more dollar till then. Of course, the market can drop insanely after that and the price of bitcoin can drop as well which means it won't work but if the price doesn't drop that insanely than you can profit easily and it doesn't even take that long.
Cryptocurrency is new for many people although almost 10 years gone to cryptocurrency but still there are a lot of people who do not trust crypto currency and think that it a Ponzi scheme and this is not good for cryptocurrency over all. I believe in cryptocurrency but when I see the big investors manipulation of the market. I dont want to put my money in it because my money if not for losing so easily.