“If one does not enjoy meditating on concentration and is unable to put an end to the laziness which delights in what is at odds with it, one will not be granted entry, from the very inception, into concentration and even should one obtain it once, it will swiftly decay through being unable to maintain the continuum. Hence, putting an end to laziness at the beginning is critical.”
From The Medium Treatise on the Stages of the Path to Enlightenment by Je Tsong Khapa
As translated in: The Middling Stages of the Path: An explanation of the training in calm abiding, which is of the nature of a dhyana by the Noble Tsongkhapa. Calm abiding section only. Translated by Ilia Durovic. Download the PDF here.