Newbies should be very cautious before investing large amounts of money at the ATH of any asset but more especially cryptocurrencies because they are among the highest volatile assets available.
Newbies should not invest in anything risky until they know exactly what it is about, FOMO is their biggest enemy, and ignorance is a sharp sword hanging over their heads. But I also think you misunderstood a bit what @aysg76 meant, because I don't see him advising someone to invest large sums of money, but to try to learn something from the mistakes others have made in the past.
They should DY(T)OR before investing, only invest what they can afford to lose and don't except more guarantees than in a gambling game. BTC and the crypto world won't earn anything good in the long run by creating disappointed, frustrated and angry people.
Any investor in Bitcoin (and even some altcoins) who invested a few hundred dollars a few years ago, today has a significant amount of money in their possession. Investing in the long-run has therefore proven to be a very successful and profitable way, and if someone is disappointed, angry or frustrated - one should not blame Bitcoin for that, because we all had the same chances, some took advantage of them, some did not.