I think that the point is that if a person is either brand new to bitcoin or considers himself to not have enough bitcoin, then he has to buy bitcoin in order to be prepared for UP, since he does not know if the BTC price is going to go up or down.
If any person joins this market with purchases and with a belief that Bitcoin price will go up, up, up and up, it's terrible thinking and horrible start.
It is not entirely an horrible thinking and certainly, a lot of us had so many not so true ideas at the time we got started in our bitcoin investment but overtime, we have learnt a lot about bitcoin on how investment journey. from an elementary point of view, bitcoin is a volatile asset and by that, it means that within a short timeframe, we can see some up and some down which agrees with your assertion that bitcoin price does not continue to go up and up and up. but what if we consider it from a long term perspective looking at it from how far bitcoin has come? wont it be right to conclude that bitcoin has been going up and up and up to this point we are now regardless of some correction that has happened occasionally?
Bitcoin does not take a linear part and that is where short term traders or gamblers always get it wrong but in the long run, you can see what looks like a linear movement as bitcoin continues to witness ATH upon ATH. every time we see new ATH it shows that bitcoin has gone high than it did in the past.
In my opinion, the truth is that Bitcoin is a highly volatile asset. Its price can rise rapidly but it can also suddenly crash. We have seen this many times in history especially in the 2021 cycle. So investing all at once or assuming it will only rise can be fatal in the long run.
So it is always discussed in this thread that the best strategy for beginners is to buy small amounts regularly DCA. This way you don't have to worry about when the market is high or low and you create a long term holding at an average price. Of course you have to invest within your financial limits not by borrowing or using leverage. This can put you under more pressure. And why just take on the burden of pressure? Another important thing is security. If you leave a large amount of coins on an exchange there is a risk of being hacked or bankrupt so using a non custodial wallet is the safest.
So I think the idea of "buying to stay on top" is not bad but it must be accompanied by a conscious plan.