The material mind oscillates amidst the three gunas, and so at times we experience a deep longing for God and at times we feel uninspired. However, a sadhak is one who pushes the mind and intellect to harbor a deep desire for God, even when they would rather be languid and cold. Sometimes we naturally feel inspired. Other times, when we strain to become inspired, even when we don't naturally feel so, that is sadhana.