This is still the most common mistake among newbies. People buy their bitcoins on coinbase, circle, or any of those sites, and they almost never do any other research than that, they think they are set and it's safe to leave the coins on there. Those people will learn the hard way.
Referring to what you say "newbies", im not newbie in bitcoin, I used it around 2012-14, just didn't use it the last years, infact I have joined this site before you did
Anyways, the money I have on coinbase is just for spending purpose and not keeping.