Discourses, "On Attention" (§1)

“When you have remitted your attention for a short time, do not imagine this, that you will recover it when you choose; but let this thought be present to you, that in consequence of the fault committed today your affairs must be in a worse condition for all that follows. For first, and what causes most trouble, a habit of not attending is formed in you; then a habit of deferring your attention.”