Objections are healthy. When someone is being offered a new opportunity or product, it's not unusual for there to be objections.
These are issues, the missing feature or unwanted element that's keeping us from saying, "yes."
On the other hand, an excuse is merely a wild goose chase, something that people say to make the salesperson go away, to minimize the seriousness of the opportunity, to hide.
Objections, then, are a truly productive way for a salesperson and a potential customer to interact. "If we can figure out a way through this objection, does the rest of it sound good to you?" An objection is an invitation, a request for help in solving a problem.
Excuses, on the other hand, are merely fear out loud.
Not only are smart and caring salespeople attuned for the difference (and practiced at telling them apart), so is the self-aware buyer/student/patient/investor/customer. Knowing what's holding you back is a smart way to go forward.
