It is not. There is no sure way to commit suicide, but cutting is less sure than other methods.

Suicide methods for men vary from country to country. In Hong Kong, for example, jumping from tall buildings is the preferred method. Whereas in the United States of America, men prefer to commit suicide by means of shooting themselves in the head with a gun.

Hanging, shooting or jumping of a high building

See link below for an Answers.com article on the most common ways that suicide is attempted. This is entirely for academic purposes.

A suicidal threat is when a person threats against themselves to take their own life.