As a matter of fact, it's very unsafe to depend on a single coin. In otherwords, invest into more than one token by spreading your investment into potential coins but be careful not to invest into pump and dump coins. Above all, make sure to maintain risk management in which ever crypto asset you are investing in.
If this is Bitcoin, it will no matter if you are only having and holding Bitcoin. For sure, Bitcoin is the best crypto investment.
But, if you are also investing in altcoins with your money, never put all money into one bag. You must have a good diversification on altcoin investment. But this is also quite tricky because you must ensure that all your invested altcoins are top coins, promising, potential, and trusted enough for investment long term. That is why I always get myself to put more money into Bitcoin.