This is an advice that can easily be wrongly interpreted, since it's very hard to know which are the "good coins".
* CMC and such mostly shitcoins listed
* Studying which coins are indeed good need a lot of time and, imho, at the point one knows if a coin is good, he's no longer newbie. I'll add that studying is somehow in the list already, but most don't have the patience for it
* Altcoins can easily die off even if they've started as a honest and good project, just because the team was too small and life things broke it apart (although the usual reason is greed).

Better advises can be:
* if you are not sure, stay away
* be extremely wary on altcoins and new services
* never forget that something too good to be true is usually bad business (scam)
* if you don't have patience to learn, stick with Bitcoin