If one is utterly destitute, with no prospect of ever being otherwise, then it sort of falls into the same category as a terminal ilness. In which case it might be a rational decision.
But I am not talking about straightforward poverty, I am talking about being completely and utterly destitute.
Or perhaps in a physical situation from which there is no escape and a painful death is certain anyway.

That's a question that can only be answered by the person contemplating this.

If you're truly healthy, how could you be unhappy? Physically, emotionally, mentally healthy people would probably never even consider it.

Would be certain that if they did kill themselves that they were not healthy because some chemical imbalance in their chemical makeup was telling them to end the process.

Hmm... Interesting question. Mostly it's the framing that throws me. Is it "reasonable". Mmm...
Well.. does one "reason" one's self into existence in the first place? One can have any kind of a reason for doing a thing, and for them, it is reason enough. That being said, I would generally presume that such choices arise from some kind of despair, hopelessness or boredom. These things are usually the result of changeable conditions.. as a compassionate person I would admonish the individual in question to try changing the condition before assuming it to be irreconcilable... If they were truly "healthy" enough to consider such a thing. I concede that such advice would arise from my own attachment to the continued existence of this hypothetical individual... and not from any rational place. Rationally I can't make an argument, because it all hinges upon my opinions of what may be better for the subject ( i.e. existence is good), or others (i.e. one is useful to society.).

I believe in quality of life , but was surprised when I learned my Mother felt that way as well . As she aged , she began saying light-hearted things about what to do with her after death , like put me in the ground and plant a tree over me , so I will at least be feeding the tree . Later in life , she told me , she didn't want to reach 100 . Mom developed both diabetes and alzhimers , and died naturally . in the hospital , at the age of ninety nine and a half . It wasn't suicide exactly , but I do feel she planned it that way .

Yes it can.
The idea that one must be depressed or suffer mental illness for opting out is errant.
Simply having life doesn't mean one has to participate.

I am planning to put together an "exit cocktail" to have on hand if/when the shit gets too thick, and my logical mind tells me the trouble to stay above ground is more than what I'm getting out of it. Seems very rational to me.

I absolutely believe it can. I believe that if you have any disease and it's incurable and or painful, you should be assisted with a dignified end. Try the therapy, sure, but sometimes it's too much. Who ate we to decide what others can bare? How can we be so selfish that we make others suffer for our own edification? Mental health issues are medical issues, with physical causes and some are incurable and unbearable. I believe a person should fight for life, but it should be a good quality life. Living in pain or in a coma isn't really life.

Yes. Being clincically depressed and treatment resistant is, from what I've heard, like torture.

No, but it's awfully sad.

Back when I was trying to "believe" in my aprents religion suicide was a consideration I contemplated. One of my sisters attempted suicide twice due to presures from religion.

Over all, I tend to agree with the assessment that "suicide is a permanent solution to a temporary problem."

Healthy persons who contemplate suicide have psychologically boxed themselves in to where suicide seems to be the only way out. This is usually the result of living a life to fulfill other people's wants, needs or expectations rather than findign out what one wants for oneself, and basing one's self worht based on what others think instead of what the individual thinks.

The way wout of hte box (other than suicide) is to devalue what the opinions of others and what others think and to start thinking for oneself and develop vlues of ones own, rather than let other decide for you, what you shoudl think or wha tyour values should be.

Until one learns to think for oneself, or as one is lernign to do so, you just put off suicide, as it is always an option, but a pretty final one that cant' be taken back. It is interesting that every single person who jumped off the Golden Gate Bridge and survived, chamged their minds on the way down. None have jumped a second time.

So, in my mind, suicidal thought are mostly a result of lettingothers make decisions for you, rather than thinking and making decisions for yourself, without regard to what others want you to do. Breaking out of hte psuchological box, can be gradual as it was for me, or it can be immediate as it happened for those who jumped off the Golden Gate Bridge. In th eend survival is instinctual. We just need to rid ourselves of the fellings of guilt shame and fear, which has been instilled in us to bend us to the will of others.

Since life is a terminal condition that everyone contracts at birth it could be argued that self-terminating could be a rational decision and also be equally argued that it is not.
Personal I would assume that cutting short your life deliberately when not suffering a physical condition that reduces the quality of life to unbearable indicates that you are in a mental state causing an either greater or equal state of suffering (either consciously or unconsciously) and therefore is not a rational choice, though the person concerned might think it is.
The only reason I personally can discern for such an act would be one of self-sacrifice where the action of suicide would save the lives of a greater number of others. (E.g. see the end of Star Trek 2, the needs of the many outweigh the needs of the few or the one.)

It's a very personal choice and nobody can answer that question for the person contemplating. I would try to talk reason with this person and would be sad if the decision would be to leave this world.Who can truly understand what is going on in the person's mind!?

Well even given your disclaimer you should ask yourself why you are fascinated by it. Any therapist would immediately flag this as a warning sign.

To the adult, of course, it is.

From a biological standpoint, suicide can't be rational. Our brains are programmed to survive, not end our own lives. The amygdala produces the fight or flight response when it picks up a threat of harm, which causes us to automatically act in a way that will prolong our existence. Suicide contradicts this and requires significant mental effort to overcome. This is why we don't jump into oncoming traffic anytime we have a bad day. We are designed (by evolution, not a god) to exist and make more babies so that we do not become extinct. I am a military therapist and work with individuals endorsing suicidal ideations everyday. Fortunately, I have yet to lose a patient to suicide, and while I know colleagues who have, there is a reason that the numbers are relatively low in proportion to the number of people who report wanting to do it.

It is unfortunate that a life can be spent in such a wasteful manner because to have existed is such a great honor. However there are those who feel so despondent that they terminate this gift of life. This is a great shame but there isn't anyway that we will be able to prevent such waste.

No, it's not reasonable. Can they do it with no judgement from me? Yes. Is it reasonable? No.

Of course it's your life but the people around you should be able to say goodbye

Suicide is never reasonable. Unfortunately for some who are in the depths of despair and feel there is no way out, it feels like their only option. Mental illness, trauma, abuse, that goes untreated can lead into some very precarious places. I've been there, I know. I also know there's hope and healing.

Please it's never so bad that suicide an option

No they have psychological issues and need help.

Most of life's downs are temporary, death is permanent and the end of everything. I would never pull that trigger. Here is a thought before you do it wait. Go to bed and set your alarm for 5am Get up take a shower get dressed, grab some coffee and grab a chair. Take it outside and listen to the sounds the morning makes and watch the sunrise. Ask yourself, is nothing better? If the answer is yes keep doing that every morning until you say nothing isn't better. You owe it to yourself to keep trying.