Why Positive gives happiness and negative gives unhappiness?

Positive Effect of Positive Words

A man once asked me, “When will my speech become as pleasant as yours?” I told him, “When all the negative words that you use, you stop uttering, then your speech will become pleasant.” This is because each spoken word has its own inherent quality and phases.

Always speak in a positive manner because there is a Soul within the person you are talking to. When something positive happens, it is wrong to say anything negative about it. All these problems arise because one states the negative in that which is positive. And whenever you say, “No harm done,” the instant you say this, tremendous changes take place from within. So always speak positively.

Nothing negative has happened to me for so many years. I have never experienced even the slightest negativity in any circumstance. If your mind becomes positive, you become divine, which is why I tell people to get rid of their negativity through maintaining equanimity. Then only the positive will remain. In your worldly affairs, stay positive. In nischaya, the real, neither the positive nor the negative exists.

Reference: Book Name: Science of Speech (Page #9 -Paragraph #3 to #5) 

Only the positive will give happiness in the world

There are tape-recorders, transmitters, and many other instruments today. Prominent people live in fear of someone recording their conversations. These instruments record only words, whereas the human body, and the mind is such that it can ‘tape-record’ everything. People do not have fear of that. If someone is asleep and you make a comment, ‘This man is useless,’ your comment will get recorded within him and it will later produce its fruit. Therefore, you should not speak evil even of those who are sleeping. You should not utter even a word because this machinery is such that it records everything. If you must say something then say something good. Have a good inner intent and you will be rewarded with happiness. But if you say something even slightly negative, even in the dark or when you are alone, then its fruit will be bitter like a poison. Everything will be recorded, therefore record good thing.

Questioner: I do not want bitter fruits at all.

Dadashri: Say negative things if you want bitter, otherwise do not say it. Do not say anything negative about anyone even if that person hurts you. Tell him, ‘I am grateful to you.’

The Lord has said that if someone insults you, invite him for dinner. Pardon him even if he has so much wildness. You will be drawn again into worldly life if you try to take revenge against him. You should not try to avenge yourself in this time cycle. There is nothing but wildness in this Dushamkaal—the current part of the time cycle. You can never tell what kind of thoughts will come to you. Thoughts about the whole world will come. The living beings of this time cycle are going to collide a lot. You too will also have to collide if you create enmity towards such people. That is why we say, ‘Salam Sahib’ (i.e. we must remain superficial in our interactions with people); in this time cycle you should forgive people immediately otherwise you will have to suffer. And this world is based on this enmity.

It is impossible to reason and try to make someone understand, in this time era. If you know how to explain things to them, then do so using good words so that you do not become liable even if it is being taped (within the other person). Therefore remain positive. In this world, only the positive will give you happiness; the negative gives tremendous misery. How much liability there is!

There are only two things: Positive and negative. If we are negative then whom will the nature help? Negative should not be there in our dictionary. 

Reference: Dadavani Magazine Sep 2009 (Page #20 - Paragraph #9, Page #21 - Paragraph #1 to #7)