Positive thinking means the conscious choice to be happy and positive. Happiness is not a condition of the mind, or a goal, or a dream, it is a choice that you must make every day. When you wake up in the morning you have several choices: to be happy, to be sad or to be in between. Most of you make that choice unconsciously and this leads to questionable results.
Positive thinking can be reasserted by seemingly mundane choices in your life: the movies you watch, the songs you listen to, the books you read, the people you hang out with. It can help you be healthier, more productive and ultimately happier. Yet for most of the people it is hard to put optimism fist.
Negative thinking on the other hand is very easy to achieve. The human mind has a strange tendency to get pulled into negativity and self-criticism. Once in there, it could be very hard for you to pull yourself out of it. Your self-esteem and self-confidence suffer when you dwell on the negative things that others say about you, or that you think about yourself.