That's correct, but it's not how human psychology works. ATH brings enthusiasm, ATH brings FOMO, ATH has bigger chance for one to open his wallet. If he has the patience to get over the next "crypto winter", he has won.
On the other hand, in a bear market people tend to wait and wait and wait again for lower price, then they're fear the price will never rise again, then.. oops, it's ATH again. And this is how some find reasons after reasons for staying away.

While I agree ATH is not a best moment to invest, if one made his mind, best is to DCA, whether there's ATH or not: buy multiple smaller amounts over longer period of time. This way one will clearly not buy always at ATH, this way one may even have the opportunity to buy the dip and the overall sentiment and investment may look really good. But, again, one has to be sure on what he's doing, one has to understand bitcoin, from what limited supply means to the market wild fluctuations and wallet security too.