why du people feel sad

people feel sad because they feel they have been undone ..and to all fairness they have a right to be sad..u cant be happy all the time..thats life

There are plenty of reasons why people feel sad. But most common reason in my view is that when things don't go your way you start feel frustrated and that frustration gives way to sadness. As to your theories that your sadness make other people happy is baseless unless they are your bitter enemies.

It's common that people feel sad or depressed. When they got what they don't want, they become unhappy. But they key is how to deal with the situation.