I think e I don't think non vengono mai usati da soli, ma vengono sempre seguiti da so, come nell'esempio, o da una proposizione come nel caso di I think/I don't think he went to the concert.
Festivals may be either religious or non-religious in nature. Some celebrate the patron saint of a town or the anniversary of the foundation of a church with processions, fairs, and funfairs. Others are organized to celebrate a local product with stands where you can sample local wine, truffles, chestnuts etc.