You have pointed out really important idea in investing means putting your money in different things. I will also say that it is important for people who are good in investing to not put all their money in just one place. It is good idea to spread money into different types of investments like stocks or gold or in other altcoins too.
Investing in different asset classes and different areas is indeed a good idea, but only if one can afford to do that. Someone who has good money and is ready to invest can choose multiple places where they can invest their money, such as Bitcoin, gold, and real estate. Different investment assets will give someone different exposures to both risks and rewards because they have different growth mechanisms, and their volatility differs from each other.
Those who wish to get more profits within shorter periods of time will choose Bitcoin because of its extremely volatile nature. Those who prefer a bit of stability and don't want their investment to lose much value will go with gold, and those who want both good profits and stability for the value of their investment will get into real estate, and finally, someone who has enough money as I said and a good risk appetite will go for all.