For those who haven't been in such situations it is hard to imagine someone can be so desperate that they consider taking their own life.
People can be hard and cruel. Others should stand up for those who are being bullied, but you have to be a strong person (physically and mentally) to stand up against the bullies. But you can always help the ones that are being bullied.
There is also a recent trend that people that feel lonely and depressed are taking their own lives. These are mostly older people. There are quite a lot of initiatives to prevent loneliness in the society, but they don't always reach these people or they do not want to be helped.
A difficult subject indeed...
Most of the time, bullying and harassment are the key elements for someone to make such a drastic decision, as well as loneliness. Rarely is it due to illness, some ask for euthanasia.
But yes, even in all those possibilities it is quite sad, we will never really know what was in the mind of the person who took his or her own life.