Complex sentence: You first have to raise both Chen and Charlie's friendship to 5,000 friend points, this is hard to do for you cannot see the friendship bar and must be able to guess wether or not you have gotten them high enough.
Split into simpler sentences: You first have to raise both Chen and Charlie's friendship to 5,000 friend points. This is difficult to do, for you cannot see the friendship bar and must be able to guess whether or not you have gotten them high enough.