Diligence means willingness on the part of an individual to extend all his/her effort to succeed or persevere. It means always trying one's best, and not accepting excuses for failure. It means believing that almost any feat is possible, despite odds or opinions to the contrary.
Diligence is the most important quality a person can have, because without diligence, one can accomplish nothing. Not many things worth having are easy to obtain. Almost invariably, repeated efforts are required for success. Diligence makes the performance of repetitive, strenuous, and long-term exertions possible. Diligence allows one to succeed.
The philosopher Nietzsche provides an excellent example of a diligent person. Though plagued by severe migraine headaches, insomnia, nausea, arthritis, and near-sightedness, made all the worse by loneliness and poverty, he succeeded in producing great works of philosophy. Against doctors' advice, he would normally write all night long, disregarding pain and discomfort.
Examples of diligence are easy to find, because all great people are diligent people. Life is not easy, and diligence is a necessity.