"Stealing opportunities" - disagree to this. These markets are based on speculation and there are several opportunities. We must admit that we often fail to recognize them.
It is based on speculation, you are right with that, however, if you are discipline enough to hold, you should not fail because the market can be bullish as well. Just make it simple, if you hold for long term, you need to ensure a target is already in place, for example, you buy bitcoin at $19k and you plan to sell it when bitcoin rises to $100,000, then you have to hold until that time will come, otherwise, that's the real meaning of missing the opportunity.
but, first, you need to believe that bitcoin could reach $100,000, when you are convince, holding until that time will come should give you an ease.
Being disciplined enough to hold as long as you have to will bring you profit no matter what, that is a guaranteed way to make a profit in crypto world. However do not forget that we are talking about crypto and prices do go down and up and down and up constantly, which means even if you know that you are going to definitely make a profit from just holding, that is not the only way to make money and that is why people want to make some profit from trading as well.
If you could make a profit from direct increases that is great for you, but if people could make 2x more profit from buying and selling constantly everyday that would be better. Both of them are possible and none of them are a wrong way to go, it is just a difference of patience and also there are more risks involved with trading.