This is probably the most important factor to look at when deciding whether a cryptocurrency will survive into the future or not. Some cryptocurrencies, apart from acting as coins and trading assets, also provide platforms, serve as the fastest means to move money across the globe, try to solve a certain problem in society or in the cryptocurrency ecosystem, and do a lot more.
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.