A really great question, with so many answers. So many seforim and books talk about it.
To start – the Torah truths and principles do not change. לא תהא תורה אחרת, מוחלפת. They are the absolute truths. It’s about how to reconcile our actions, approach, direction to be in line with the Torah, not the other way around.
Let me begin with a “vort” I read somewhere – הקהה את שיניו – soften his bite! So prevalent, useful for today’s rebellious, defiant youths. Try to soften him/her up. There’s a מגפה out there, and it’s not necessarily the kid’s fault – do anything to get him back.
Another approach: Where the subject is far gone, we want to at least save the rest… we set a distance… we’ll have to deal with this kid later.. we need to salvage what we could. Think of an amputation ר”ל, it’s painful, awfully painful, but it’s needed to save the rest.. It IS DIFFERENT because לבל ידח ממנו נדח, eventually everyone will return.. question is when.