Attitudes changes everything. It makes a difference. Your attitude towards what you want to do will either allow you or prevent you from getting it done. Positive attitude will yield positive results. Negative attitude will yield negative results.
With a positive attitude, you can look at things with a perspective that seeks to use the situation in a positive manner... no manner what happens, and because of that attitude, you will generally grow. With a negative attitude, you can look at things with a perspective that seeks to use the situation in a negative manner... and usually, whether something good or bad has happened... it just won't be as bright and nice as it should be.
Your attitude will help mold who you are, and can also affect other people. Think of all the times someone has said something that brightened your day. One person made a difference in your life because of their attitude. It changes everything. It can not only affect the individual, but the people around them. Keep your attitude in check and give out that positive attitude towards others. It really helps.
In running, when you have a negative attitude, you probably won't run well. With a positive attitude, you could change a possible bad race into a great race. It doesn't mean that you're unrealistic and reach for unimaginable goals in the race. It means that you enter the race realistically and with a positive attitude. A 'CAN-DO' attitude brings out the best. A 'NO-CAN-DO' attitude takes away the potential you have.
Being positive can be relaxing, allowing the individual to run relaxed and therefore, at a better pace. Being positive helps you do your best, allowing optimal performance... or optimal training which leads to optimal results. Attitudes can change everything.