I firmly believe that when you are positive, you not only make yourself better, but also your environment.
Having a positive attitude does not mean that you have to have optimism and happiness. What positivity means is to always be willing to think positively and generally be more positive than sad or depressed. With sayings like the one mentioned above, it is a matter of putting oneself into the right state of mind in order to make the best use of the opportunities of life.
Of course, positive thinking does not mean completely ignoring bad or unpleasant feelings. It just means that you approach unpleasant things in a more positive and productive way, and instead of seeing everything as a victim of negative circumstances, you see it as an opportunity to learn and grow.
Self-talk comes from logic and reason, while other self-talk can arise from misconceptions created by other people (e.g. your parents, friends, family members, or even yourself). Negative attitudes arise from thinking negative thoughts so much that they become habitual and become part of your subconscious and part of your personality. When you’ve had a negative attitude for so long, you may not realize you have it, but it’s there.