That "belief" is becoming more and more like data each halving. Many people "believe" that we are going to have ATH about within one year of the halving, that means by 2025 spring or so we are going to see above 68k, or before that date of course, that's also possible. This is just a "belief" at the moment, but when enough people believe something like that will be true, it becomes a bit more like data instead of just a belief in people.
The basis for this belief also has clear reasons because everyone has seen the previous data and refers to the reality that happened previously in Bitcoin when the market was very bullish until the creation of a new ATH. And it could also be that conditions that are getting better at this time will become a reference for everyone to continue to believe in Bitcoin and will continue to increase everyone's confidence in owning Bitcoin before and after the halving occurs.
Why does it become like data, well when you get a huge group of people who believe that it will go up like that, then it is obvious that you are also talking about a lot of people who are willing to spend their money to buy, if you think it would go up, why wouldn't you buy right now, and when enough people spend enough money like that because they believe it will go up, that makes the price go up, and when the price goes up, suddenly they were right about thinking that it will go up, they made it go up by thinking it may go up.
Who says I don't buy it now, in fact I made the purchase before Bitcoin experienced an increase like now because I have long been very confident in Bitcoin that the very real price increase will return to Bitcoin so I never thought about other people's beliefs in Bitcoin because I have my own confidence in buying Bitcoin by taking advantage of the price decline.