Explain the pitfalls
They may face pitfalls but rather explain it to them before it's too late.
I think children should be protected - and whilst we protect them, we explain the possible pitfalls of situations (age appropriate of course). We then arm them with alternatives, realism and a sense of objectivity required to make sound decisions. Protecting your kids all their lives is not a bad thing. Your protection changes as they grow up. For instance, if your grown son wants to buy a new car, but clearly you know that they will have a tough time with the repayments, insurance and maintenance on a more expensive vehicle. All you can do to 'protect' them, is once again, to explain the pro's and con's. At this point, it is essential to let go and let them make their own decisions, whether you feel they are mistakes or not. To want to protect your child is an act of love and care. Children adore it, then they reject it, and then they come looking for it later on. They protect us, we protect them - it is a win-win situation, a situation of mutual love, respect and care. At the end of it all, therefore, you end up teaching them to be protectors themselves.