Maybe you remember when, thanks to The Wall Street Journal, everyone thought the SEC was going to meet on May 7th to decide whether or not Ethereum (ETH) was a security. If you had taken up a large position in ETH prior to the 7th, you would have been disappointed when the price fell from ~$793 USD to ~$743 USD amidst news that there actually was no meeting after all.
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.