What does the professor mean by this statement:

M1: Managers must manage．It’s a simple statement, but let’s think about what it means for a minute．Let’s ask ourselves, what makes a manager? Tammy?
W: A manager is someone who supervises other people ..．and plans and carries out projects.
M1: That’s right．A manager has the ability to set goals, and then to accomplish what he or she sets out to do．Business managers shoot for results．This means that once you set your business plan and budget for the year, you have to achieve the sales, the market share, the earnings-whatever you set out to do．Yes, Doug?
M2: But even the best managers can’t achieve every goal．A lot can go wrong that’s beyond your control．Say, for example, the whole economy goes into recession- that would interfere with your goals, like your sales, for example．Sometimes things go wrong, no matter what you do.
M1: You could say that about life in general．We’re always being hit with things that are beyond our control．But good managers have to adjust to changing circumstances．They ..．they have to ..．but let me share a story I tell all my students．It’s about two promising young people of equal intelligence and ability．Both are college students, and both want to go on to a top graduate school of business.
The first student, May, hands in all of her assignments and does exactly what’s expected of her．She receives good grades-mostly As with a few Bs-during her first couple of years in college．But then one year she gets the flu before final exams, and she performs poorly on her exams．As a result, her grade point average slips to just above a C．May tells herself that it wasn’t her fault, it was because she wasn’t able to study when she was sick, and she vows to do better next year．But something always happens to wreck May’s plans．Next year she misunderstands a question on the final and gets a C．May graduates with a B-minus average.
The second student, Kay, also wants to go to a top school, so she sets out to get an A average．She studies four hours every night．Her diligence and hard work pay off, and she gets all As her first three years．Then, in her senior year, she runs into trouble with one of her courses, advanced accounting．She works hard, but the material is difficult, and she has a hard time solving some of the problems．At midterm she’s struggling for a B．She works harder, does some outside reading．She asks her professor for help, but the professor doesn’t have much time for students．What does Kay do? After trying several different approaches-studying harder, reading more, asking for help  what she ends up doing is finding a graduate student to tutor her．She works long and thinks hard．And, of course, you know the end of the story: Kay gets her A．Now, what kind of manager is each student’?
W: Kay is certainly a more successful student because she got all As.
M2: The first student, May, probably won’t get into a top business school because the top schools require you have to have a high grade point average, and she didn’t have that．So the other student, Kay, has a better chance of getting a top-notch business education.
M1: What you both said is true．But who’s the better manager: May or Kay?
W: In my opinion, May wouldn’t be a strong manager．She just drifted along．When she got the flu and blew it on her exams, she never really caught up．Kay is clearly the better manager.
M2: I agree with Tammy．I think Kay will be a better manager．She graduated with an A average, so that shows how hard she worked, but she also knew what to do when she was having trouble in her accounting course.
M1: Kay was a manager before she even reached business, school．She had grasped the essentials of good business management-not because she worked so hard, but because when one action failed, she tried another, and another, until she achieved her goal．That is what managers do.