Cryptocurrency is volatile! There is always the chance that the market will crash, or that you will face some other catastrophe. Cryptocurrency isn’t a centrally controlled and regulated fiat currency. If you lose a coin, or someone cheats you, or your account gets hacked, there is nothing you can do about it (which is one reason why you want to have 2-factor authentication set-up).
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.