Sales opportunities are always around the corner. Sometimes these appear as unplanned sales meetings, unsatisfied potential customers, happy customers, or unexpected calls.
As told, these are unplanned and unexpected, so these are more likely to get ignored by the reps. That can happen as one might be in the middle of some task, meeting, or else.
A good sales rep is always in search of sales opportunities. No matter the condition, the only rule they must follow is Look and Seize.