Probably the single most important factor of any success is the ability to show up day after day and do the right things.
The person, company, or team that is unable to deliver disciplined actions is going to experience ups and downs.
In sales, lacking discipline is going to negatively impact your presentation, motivation, ability to predict results, follow-up, and your ability to keep your pipeline full. Lack of discipline is rampant in sales because so many sales positions are commission based. This allows the salesperson to believe he or she can self-manage and get away with spotty undisciplined activity. The economy will discipline anyone who operates with this sense of freedom.
If you want sales success, you must exercise discipline.