I don't think that...
Always followed by the subjunctive in Spanish — a key grammar point. No creo que sea verdad = I don't think it's true.
I don't think it's as complicated as it seems.
I don't think she'll come on time.
—Will it work? —I don't think it'll work like that.
I don't think he'll come today.
I don't think it's a good idea.