Suicide, at the end of the day, is kind of a gamble. Nothing is 100% effective. Compare it to surgery, where there's always a risk of complication, no matter how small.
If we want to do it, all we can do is try to research a method that's highly effective and will get us where we want to go.
I'm personally looking into inert gas. If everything is secured in place, it's effective and painless. Most threads of failed attempts using this method seem to stem from someone falling out of position and being severed from the gas supply/breaking the seal on their mask/hood, or from not having enough supply and running out of gas and surviving as they were not sufficiently asphyxiated.