Your teenager is about to make a mistake .You made same mistake as a kid and learnt your lesson,which helped you in your adult life.
Will you let kid make the mistake so that he/she can learn well , or will you advise beforehand to prevent it?
Why ?
Is this “Need answer fast”? 
Both. I’m gonna explain to her why she shouldn’t do this stupid thing, because I’m her mom and that’s my job. I’ll do it with the understanding that my warning is unlikely to prevent her from doing this stupid thing, because she’s a teenager and doing stupid things is her job.
What Diana said. The good news is that they listen and learn. The bad news is that it takes them until they have kids of their own to do it (says the grandma who gleefully listened to her daughter gripe about the psychotic demon who’d been left in place of her formerly angelic baby). 
No!
I will advise, wheedle, nag, proclaim by fiat and if possible, lock my children in their rooms. I will do this again and again, all the while knowing it’s useless.
We tell them not to do stupid things, they do stupid things. It’s the way of the universe.
I had to learn the hard way not to leave that hooker’s body in a shallow grave in Reno, and they will too.
Seriously, I try to go with the “let them figure it out for themselves” route because I know people whose mothers have always gotten them out of stuff and it is definitely not pretty in adulthood. If it were a stupid mistake that would have life changing consequences I would probably step in - I’m thinking of something like forgetting to unpack the car after the weekend hunting and ending up with a weapon on campus or being too embarrassed to ask about condoms. But just normal stupid teenager shit? Yeah, they can dust themselves off.
What bullshit.
Not everyone grows up just because they had children. Some of us manage to pull our heads outta our asses long before the breeding begins.
I try not to let my kids make obvious mistakes while I have a say-so in their lives. They will be out on their own soon enough and are free to learn things the hard way then.
I think that the best thing to do is give them as much honest and accurate information as possible upfront, and then not let them do jack shit. They’ll still do it, but they’ll be informed.
I concur. I wonder how many times I don’t heed the warning of my mum just because she go about it in a hysterical manner. Even when she is right.
Exactly. Except my parents were opposite. I knew them to be reasonable and non-alarmist. If they warned me about something, I took it seriously.
I think the only thing they ever actually flat-out forbade me from doing was riding a motorcycle.* And when I became an adult, they asked me to please not do it. I’m 38 and I still haven’t ever been on a motorcycle. I figure that they only ever asked me not to do that one thing, so I’m happy to accommodate them.
That said, I agree with the others–my response would depend on how serious the consequences of the action would be.
*Please don’t hijack this thread into a discussion of the relative dangers of motorcycles. My parents’ request may or may not have been logical but I’ll honor it in any case.
I always give them the examples from my life so they can at least be forewarned. Whether they pay attention and take it to heart is a totally different matter. Both my son and I have ADD. I know exactly the kinds of problems he is experiencing and told him about the tricks and tips that helped me at school and now at work. Sometimes he listens and I breathe a sigh of relief. Other times he ignores my advice and I hurt for him and for the fact that I can’t solve his problems for him.
To not warn your kid is cruel. It’s tantamount to not putting warning labels on items.
“Hey, Bob. People keep getting electrocuted when they use our hairdryers while in the tub. Should we tell them not to do it?”
“Fuck ‘em. Let ‘em figure it out on their own.”
I would try and help my daughter not make the same mistakes - that way she can make new ones!
Seriously though, explain WHY - many parents don’t tell their kids the WHY…
Exactly! I made mistakes, God knows. I still make mistakes, and will continue to do so for the remainder of my life.
But I can give my teenage/young adult children the benefit of telling them what I’ve learned, how I learned it, how maybe I didn’t learn it (just outgrew it) but only 'cuz I got lucky. . .
I’ve been very open with my kids about my past; mistakes as well as successes.
What they choose to take from that openness is completely up to them!
I am of two minds about this and here is why. Two of my kids are still at the age where they wonder how dad or mom knew about what they are trying to do. It is still at the fun stage when they get busted by me.
My oldest is 18, living at home, going to college and I feel that it is a little more important for me to be active when I know he is about to make an error. Sometimes things that would be a small bump in the road for a minor wind up being a big deal and it’s consequences could follow you around forever when you are 18 and considered an “adult”.
On preview I see Norine W (I remembered for a change :)) has said it well.
I will do all I can to keep my teenager from making the same mistakes I made. Some were real doozies and I was just lucky the consequences weren’t far worse.
Of course, maybe they can learn the lesson through your own mistake without having to go through it themselves.
This.
The best time to make a mistake is when they live at home. I do mention alternatives but it goes in one ear and out the other. Kinda cute though when they get married and have kids, then you start hearing then say things you told them years previous.
And many parents who tell their kids the WHY get lengthy feedback about why that particular WHY doesn’t apply to them or their situation.
Give good information, intervene if the consequences of their actions may be too dire, and be ready to pick up the pieces. Also be ready to congratulate proper thinking and actions.