When a friend brings a serious problem to you, it may be tempting to minimize the problem so you don't have to deal with it.
Your first impulse may be to say, “Oh, it's not that bad” or “Don't get so emotional about it” or even “This isn't that big of a deal.”
However, this is usually the last thing that a struggling friend wants to hear. Even if it's objectively not a big deal, it FEELS like a big deal to them (or else they wouldn't have asked you for support.) Meet them where they're at. If it feels like a big deal to them, treat it like a big deal.
You also need to avoid the temptation to minimize their problem by blaming them for it (“I'm sorry you're stressed about your bad grade, but it's your fault for not studying.”)
Sometimes people do cause their own problems, but even if the problem is 100% their fault, it doesn't help for you to point them out. Your job is to be a supportive friend, not to assign blame.
So give them space to express their feelings. Help them explore why this feels like such a big deal to them. You may want to gently provide perspective – perhaps reminding them that even with this problem, there are still a lot of good things in their life, or encouraging them to see that the current problem is temporary.
But don't tell them what they're feeling is wrong, or that they just need to “get over it.” Accept that their problem is a big problem to them, and support them without trying to correct them.
Next: Don't change the subject