Theirs no cryptocurrency investor that doesn't know when to invest and when to look after market, even though you don't have capital to invest that moment and you have see coin you like to invest, you can invest on the coins directly by selling your coin and purchase the new one, so I believe that in cryptocurrency investment someone have interest on other coins has other investment already, so rich people also have the same pain you're emphasizing on, but what I know quite well is that anyone who is cryptocurrency investor have so many coins it invested on, when exchange list a coin it can swap to the new coin that it wants or needed mostly, but a process whereby you're not a crypto investor you can't be able make such instant swap.
If you are an investor then you should be calculative of all the periods that you will be able to invest and the moment you have already invested it will make everything very easy for you, and that is why you need to have knowledge of what you are doing and in the process of acquiring you will be able to know when exactly to invest or not and sometimes I even feel that the capital is more important than knowledge because after the knowledge and you don't have capital then they are all useless the best thing I will do is to get capital then next I will get the knowledge to make things easy for you.
If you are able to sell the one you have to make a high profit then you can go for other coins, people don't want to rely on one coin and I don't blame them you have to know how to take advantage of the market because every coin have their own potential, the market is alway open and you have to be the one to choose wether you want to invest in a particular coin or not and your research will determine which one you are going for, and that is why you have to take your research seriously before investing.