In my opinion, everyone has gone through a moment where they wonder what would happen if they suicided and how things would continue or end if they ended their own life.
I believe any normal person has considered suicide an option. There are just moments in life that you'd hate so much you'd think about it. Actually going through it is something of itself.
In my opinion, suicide is selfish, as you escape and harm others around you as a result. Family friends and people who knew you are affected by the suicide so you were selfish to escape from your problems.
I think suicide rates get higher as one ages, since some people find their life meaningless as they age and people forget about them or live their own lives and feel they can't do things as they age.
Some people consider euthanasia to be suicide since they make the choice to end their life to end their suffering, which is why I hate the discussion of religion brought into things like this as the ultimate "write-off" to a discussion.
Or as Aleex has said, "cowardice" may bring some to have euthanasia done to them out of the incapability to end their life.
I don't think there's just one sole reason why someone commits suicide; I don't look at it as something someone chooses just to fit one thing, they make it for balancing and weighing what "ifs" they do it. What's apparent is that some people commit suicide to make debts vanish for their loved ones or to gain life insurance funds for their loved ones because they are worth more dead than alive.
At some of these moments, is there ever really a "right" answer? I think the best you can do is try to convince the person it is better to live and how they'll affect those around them that care for them than just saying "its wrong" Some people just simply can't be helped in their mind and choose to end it.
Suicide is a complex issue and many will just paint it as a black and white scenario.
There's more to it than just hearing/reading about it, try experiencing the scariness of what a person thinks when placed in it. Some people are probably just screwed in the head, but its impossible to know how each person is and how they'd react if things hit them.