Will power and desire alone cannot sustain your performance over the long haul. These are false premises that ignore the scope and complexity of your process of adjustment and adaptation. Mental and physical endurance require gradual conditioning. Approach conditioning not as if you are trying to smash your way through an enormous wall, but as a gentle pastime by which you can coax a slow, continuous stream of adaptations within your mind and body. It is the enhancement provided by these adaptations that allows you to endure through stress, pain, and suffering—not your strength of will.
You are capable of more than you know. Choose a goal that seems right for you. With self-discipline, persist to the best of your ability, and resume effort following setbacks.
Condition yourself, and endure. The world needs all you can give.