As with many things in life, acknowledging that there is a problem is often the first step in recovery - and sometimes the most difficult.
Stigma - Coming to a point of acknowledging that you may suffer from a mental illness is a tremendously courageous thing to do - and many are afraid to do that. There exists a social stigma about mental illness that often makes it harder to acknowledge than physical illness.
Swallowing your Pride - Acknowledging that your words and your actions may have hurt others is equally difficult. There may be reparations to make. You may have to turn from blaming others to blaming yourself. It takes great courage and humility to do this.
Fear of the Unknown - it's normal to feel afraid of things which you do not understand or know well. When it comes to seeking help for a mental illness it is even more so. Baring your soul to strangers who will analyze you, observe you, possibly judge you. Possibly spending time in a mental health facility or coming into contact with other mentally ill people. Taking medications which may have unwanted side effects. These are all frightening ideas to most people.