How to Deal with Moodiness?

Well, I have several  questions to begin this short writing:

How could actually moody exist?

Why being moody does totally get you annoyed?

Why being moody eventually a disaster for most of situations?

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Moody is a complex feeling which can ruin your day even for a second. Perfect! Perfect disaster!

In moody situation, you can laugh for 5 seconds and the next second you can cry for the whole day. Crazy!