The thread was at best self complacent and as a mother of 4 ternagers, one who is luckily on the other side, I can honestly say you don't know and cannot know what's going to come your way, no matter what the young person is like.
As a parent, you will be extremely lucky if between 13 and 19 amd especially with more than onr young person in the house, you will be completely exempt from at least one of these: heartbreak, toxic friendships, difficult teachers, struggling with a subject, illness (mental or physical), stress, bad decisions, alcohol or substance abuse, sexual harassment (sadly), this isn't even a comprehensive list.
Many teennagers will struggle when hit with one of the above and it will either be being open and honest or they will have meltdowns, be rude and not choose to tell you what's going on.
And even when all looks rosy, you don't know what they are hiding. Trust me with 4 teenagers I really have heard it all and in many cases the parents are blissfully unaware.
And even if you win the lottery and your teen is an absolute saint, then there is university. They will hit difficulties there and just because they are 19 or 20 or 21 you will still feel the same or worse you won't know.
So I just.view it in this way, it is a phase. The thead reminded me of those parents at baby group telling you that theybwere so lucky as their babies always slept through whilst you were surviving on 2 hours sleep. Or that their toddlers never had any meltdowns but you could see them hitting everyone but no it was never them :)) they were provoked!