Diversifying your portfolio is not about whether you can predict market movements but more about keeping your risks on the lower side. The idea is that a bigger part of your investments should be in lower-risk assets (if we're talking cryptos only, that means top cryptocurrencies, preferably top 10 by market cap) and a smaller percentage of your portfolio can be divided between higher-risk cryptos if you want that, such as smaller and newer coins and tokens. This way, if for example one of the tokens you have invested in completely crashes, your capital will not suffer excessively because there are the other investments that can keep it going.