This is my take on sui cide, or euth anasia if you prefer.
Everybody and every living thing in nature wants to live. And everything is going to die. It's just a matter of time and circumstance.
An old dog in the wild one day just won't be able to get up any more and will either be attacked by something else or die of hunger or thirst, or whatever else ails it. The point is it will surely die.
We differ from other living things, I believe, in that we have a capacity that allows us to anticipate further ahead and plan accordingly. But we still don't know the future, or what we will do in such and such circumstance.
Knowing I'm going to die some day and being of a kind that doesn't want to just waste away or become dependent in an intolerable situation I have made my plans, and it's really very simple. But I had to do a lot of research, because the information is hidden away in our culture where sui cide is still taboo. Hidden but searchable.
Just knowing how to die peacefully, and having the means for if you ever need it, can set your mind at rest about the whole business, so you don't have to think about it any more, or much anyway. And when the time comes, as it does for every old dog, you might find you don't need or want the means any more.
A valuable source of reading material is annas-archive dot org - Publications are usually available in different formats, PDF's being my own fav. I use a New Private Window in Firefox but I'm always on a VPN anyway.