Learn Italian: Temo abbiano troppe aspettative. - I fear they have too many expectations.

In Italian, you can optionally drop the conjunction che (that) when it introduces a subordinate clause with a subjunctive verb. This is especially common after verbs expressing thought, hope, or fear like temo (I fear). The sentence means exactly the same thing as Temo che abbiano troppe aspettative.

Would it be incorrect to include che in this sentence?

Not at all! Saying Temo che abbiano troppe aspettative is perfectly correct and very common. Dropping che just makes the sentence flow a bit faster and sound slightly more elegant, which is typical in higher-level spoken and written Italian.

Why is abbiano in the subjunctive mood here?

The main verb temo (I fear) expresses an emotion or uncertainty. Verbs of fearing, hoping, and believing always trigger the subjunctive mood in the clause that follows them. Dropping the connecting word che does not change this grammatical rule.

Why does troppe end in an -e here instead of just being troppo?