What are the hardest things about trading? (beginner's question)

Hi guys, I recently started learning about crypto trading and investing. Already read some beginner's posts and that most of the people have a huge loss in trading but still I can't really see the clear picture. (Yes I'm sure that it's because I still don't know too much about it yet but hear me out.)

For the easy math let's say that I have 25000 USD to buy 1BTC. I buy this 1BTC and patiently waiting for a few months and checking the price on every few weeks. Let's say that around the next summer of 2024 1BTC reaches over 50000 USD and when I see that the price is going down again I sell that 1BTC and I have now 50000 USD with 25000 USD profit. The next few years the BTC going down again and the next lowest point is around 30000 USD. At this moment I buy 1BTC again and I'm still in 20000 USD profit. Then again the BTC price goes up and after a while it reaches even 80000 USD. When it's happens I sell my 1BTC again and I now have 80000 USD. And if I play this method patiently in the next few decades then probably I won't make millions by it but I can make some nice extra money and I can keep going on this cycle on and on and on....

Am I missing some HUUGE information which and is this not works like this in real life? Or maybe the 95% of people loses money because the want to trade more regularly and make very bad choices? Probably I won't buy any crypto yet for a while and learn buy e-books and youtubers but I feel like now that people only mess up thing because they want tom make lot's of money, quickly without any knowledge?

Thank for the critics, comments, advices... I wish you all good trading!