Usually it takes more than one session to know.

[Topstudent]

Client: You can't help me.

Therapist: Usually it takes more than one session to know.


Is it perfectly natural to end the sentence with 'to know'? Is it enough or should more be added to the sentence?

 

[Tarheel]

It depends on the context. (See below.)

Client: I don't think you can help me.
Therapist: It usually takes more than one session to know that for sure.