I've been cutting for a long time. I sharpen knives, hollow ground scissors and wood turning tools commercially, and have used just about every bladed tool on earth to self-harm with and I can tell you that cutting or stabbing yourself to any depth, even with a freshly honed straight razor or a disposable DE blade (both of which, for the record, are much sharper than surgical scalpels) or with the point of a scandi-ground knife (which is so thin it's practically invisible) is extremely hard. Even the smallest things can make it harder; like the presence of hair, dry skin (have a hot shower first) a dry blade (lubricate it with shaving soap, warming it up helps as well for some reason) and, speaking bluntly, sanity. I mean you need to be in some kind of altered mental state if you want to do real damage. Either drugged up to your eyeballs, manic, or psychotic. The only time I ever manage to cut deep enough to leave scars are when I'm completely off my head, usually in some kind of mixed affective state. It's one of the few ways I can bring myself down and I don't even feel it. So yes either be totally crazy (or off your head on drugs) or you'd need to completely anaesthetise the area you want to cut. You're almost certainly going to sever nerves before you hit anything vital either way and this is a problem. It might even make you feel like you've succeeded and are bleeding out as when you cut a nerve it makes you feel dizzy, light-headed and extremely disoriented for a while. You may throw up or pass out. It might stop you cutting or puncturing to the right depth though as the effect is fairly debilitating and comes on very rapidly.
Consequences of failure might be very unpleasant as well. Serious nerve, organ and brain damage are on the cards and unless you really tear open a massive vessel like the carotid artery or puncture your aorta medical intervention, even basic first aid, is likely to be very effective so you don't want to try this with people around particularly as they're going to notice you spraying pints of blood everywhere. Ambulances carry saline (which will prevent heart failure, but not necessarily brain or organ damage) and EMTs can easily clamp up damaged blood vessels with hemostats especially if they're close to the surface.
The best way to do this would be to try to automate the process somehow. Most suicides I've read about that weren't accidental (or didn't involve combining cutting with huge amounts of CNS depressants) involving puncture wounds or cuts were done with tools like circular saws or nailers. Even then the person doing it was usually prone to psychosis or mania. Though I imagine it's much easier to get around your instinct for self-preservation when you only need to tap your wrist against something or pull a trigger compared to actually ramming inches of cold steel into your body. If you don't have access to something like this instead of trying to stab yourself in the neck (which, if you're hell bent on stabbing yourself, use an ice-pick or something; a knife will just make it much harder and more painful, is much more likely to sever nerves, and most people's knives are dull as bricks anyway) you'd probably be better off trying to 'trick,' yourself somehow; holding your implement of choice in line with your aorta and slamming yourself into a door (tie the handle to the doorknob so it gets pulled out when you drop) would be a lot easier than actually stabbing yourself. Especially the neck. Your lizard-brain knows where you're most vulnerable and is hard-wired to protect such places (neck, eyes, and groin especially) at all costs.
I can cut myself to bits all day long. Even when I'm sober I often test newly sharpened tools on myself (I have two cuts on my palm from a paring knife I honed a few days ago right now actually, and just as an indication of how bad knives are at cutting skin, I had to really push and drag just to get these teensy little nicks that look like paper cuts) but even at my most manic I'd never be able to bring a razor near my neck, even though I know for a fact the cuts would only be superficial, the lizard-brain just won't permit it. It doesn't even like me shaving there with an open razor.
