I caught my kid smoking pot....

This is probably one of the most common scenarios I talk about with other parents.

So, what do you do?  I don't know what you should do, but I can tell you what I've found over time.

The first thing to look at is what kind of relationship you have with your kid. I would consider:

Do they respect your aurhority?
Do you have a relationship that allows you to engage in an open dialog?
Does you kid see you as a person of integrity?
A person who can be painfully honest about yourself in order to relate to them.
Does your kid value your opinion?
Does you value your kid's opinion?
Are you relatable?
Compassionate?
Judgememtal?
Or are you some iconic distant authority that's put of touch with their world, experiences and feelings?

Don't get defensive.
Don't give explanations.
Consider these questions from the perspective of a kid, your kid.

Even if they do care they certainly can't understand all the complexities of life you balance in order to provide for them, and honestly they shouldn't have to on a certain level. They are after all kids.
Parents are just people, and I think we all do the best we can at any given time so just be honest and think about yourself the way they seem to think of you.