Suppose you’re watching BTC’s chart and notice multiple Doji candlesticks, a classic indicator of indecision in the market. You have a feeling from a few other indicators that the price is about to rise, so you buy more Bitcoin — but alas, the indecision swings the other way, and you’ve lost money (but hopefully not that much, since you’re placing stop-loss orders!).
Always pay attention to Bitcoin. Most altcoins (every cryptocurrency except Bitcoin) are pegged more closely to Bitcoin than Asian currencies were to the USD during the Asian Financial Crisis. If Bitcoin price pump drastically, altcoins price can go down as people try to exit altcoins to ride the BTC profits; inversely, if Bitcoin prices dump drastically, altcoin prices can go down, too, as people exit altcoins to exchange back into fiat. The best times for altcoin growth appear when Bitcoin shows organic growth or decline, or remains stagnant in price.