Why do you cut down your arm instead of across?

Answer 1

In order to commit suicide via exsanguination, it is desirable to create a wound that will be difficult for clotting to begin to heal. by cutting across one's wrist, there is a cross-sectional laceration of the blood vessel, whereas following the blood vessel with a knife or other cutting utensil, one can create a much longer laceration in the vessel by following it length-wise.

This larger laceration will take more time for clotting to effectively close the wound, thus increasing one's chances of a successful suicide by exsanguination. If you are having thoughts of suicide, please seek help though.