It's alright if you're not sure of the answer to this question, because there is no strict or precise "cut-off" measurement for this.  The best way to answer this question might be to examine the body of people who have taken part in therapy in the past and found it to be helpful.  On one end of the spectrum, you would find individuals with diagnosable mental illnesses (as defined in the DSM V).  And at the other end of the spectrum you might find folks who simply want to know themselves a little bit better than before, or maybe just want a 'second eye' on a specific issue they are encountering in their life.  And then somewhere in-between those two ends of the spectrum, would be individuals who may just 'feel a little stuck', 'left out' or 'disconnected', 'underachieved', 'unmotivated', 'moody', 'anxious', 'sad', or 'discontent'