When many people think of personal development, their minds immediately go to "Positive Thinking". They think of Dale Carnegie, Norman Vincent Peale, and empty optimism. While thinking positively, knowing that we can accomplish more than we currently achieve, can be an important tool of personal development, it goes much farther.
We all have freedom to dream big dreams—but when we change our thinking beyond dreaming, and move to taking control of our dreams, planning accomplishment of them, and changing ourselves in necessary areas to move ourselves toward our dreams, then we are developing personally.
Say you dream of becoming debt free. Will dreaming it make it happen? Of course not, you must realize that there are reasons you have debt. You must firmly decide to do what it takes to reduce and ultimately eliminate your debt. You must make a plan. This plan must include reducing spending and/or increasing income. You may need to find help, get some training or counseling.
By changing ourselves, we can change things in our lives. By taking responsibility for our current situation, we find out that we can really make our situation change.
Where does optimism come in? Pessimists look at their situation and feel helpless. Either they feel that they aren't responsible for situation, or that they have no power to change themselves. They look at an issue as something that always happens—something pervasive. Pessimists look at their past failures as proof that they will fail again. Because of this way of thinking, pessimists see no way out of their problem so they do nothing to improve.
Optimists take responsibility, own problem, and take active steps to change. They know they can overcome. They don't feel that they themselves are problem, but they feel responsible to find solution.
Speaking personally, I was able to shed thirty pounds when I stopped thinking of myself as a fat person and started thinking of myself as an ordinary person who needed to lose pounds.