Learn Russian: Из-за тебя нам не удалось избежать скандала! - Because of you, we didn't manage to avoid a scandal!

The verb удаться (to manage / to succeed) is impersonal in Russian. The person who succeeds or fails isn't the grammatical subject; instead, they take the Dative case (нам = to us). Because there is no active subject, the past tense verb takes the default neuter singular ending, -ось.

Why use the perfective удалось here? Doesn't the negative не often trigger the imperfective aspect?

While не often triggers the imperfective to show an action was never attempted, here the attempt did happen, but the result was failure. Using the perfective не удалось emphasizes the specific, failed result on this one occasion. If it were a repeated failure over time, you would use the imperfective не удавалось.

Could I say потому что тебя instead of из-за тебя?

No. Потому что means "because" and must introduce a full clause with a subject and verb. To say "because of [someone]", you use a preposition like из-за followed by the Genitive case (тебя). Из-за is especially perfect here because it is used for assigning blame or pointing to a negative cause.

Why is скандал in the Genitive case (скандала)?

The verb избежать (to avoid) always forces the noun that follows it into the Genitive case, rather than the Accusative case you might expect for a direct object. It helps to think of it as "to escape from something" — and in Russian, the idea of distancing from something usually takes the Genitive!