The will to accomplish something involves both direction ie the actual goal, what you wish to accomplish, as well as the amount of energy or charge behind it. Interestingly, the ascetics with whom the Buddha first started his spiritual journey were referred to as "strivers." Striving suggests a lot of energy behind the will to accomplish a goal.
The Buddha found that this striving type of effort could only take one so far. To go beyond, one needed to let go of striving and embrace a middle position - like a well-tuned string musical instrument - not too tight, not too slack - balance, equanimity.
Intelligent mental effort is not at all like trying to lift a very heavy object. It is effortless, instant, where doing & being meet. By gently, intelligently, reducing the noise of self-talk and reducing the internal friction of clinging to ghosts of the past & future, energy is liberated - there's more energy available to creatively embrace now.