The conjunction che is normally traduced with the conjunction that.

He said, that he could do it.
Ha detto che poteva farlo.

The conjunction perciò is normally traduced with the conjunction therefore.

He didn' t say anything to anybody therefore nobody knew what he was doing.
Non ha detto niente a nessuno, perciò nessuno sapeva ciò che sta facendo.

It is pretty clear therefore that che / that and perciò / therefore are completely different things. If an action / event is the consequence of an another action we use perciò. Nevertheless in one special case even in that case che / that is used. If the consequence is formulated as a comparison we use che / that.

only consequence without comparison therefore / perciò   He was drunken, therefore he didn' t know any more what he was doing.   Era ubriaco, perciò non sapeva più cosa faceva.   a consequence and a comparison that / che   He was so drunken that he didn' t know any more what to do.   Era così ubriaco che non sapeva più cosa faceva.

In the sentence He was so drunken that he didn' t know any more what he was doing the conjunction so...that describes without any doubt a consequence. He had been drinking so much that at the end he didn' t know any more what he was doing. But only in comparison the conjunction that / che has this semantical value. We are going to see a similar problem in chapter 16.2 intention.

But it is evident that in both cases the consequence has a cause because both sentences can be transformed.

Because he was drunken he didn' t know what he was doing.   Poichè era ubriaco, non sapeva più cosa faceva.   Because he was so drunken he didn' t know what he was doing.   Poichè era così ubriaco non sapeva più cosa faceva.