In my personal view, it is a wrong way to disuade students pursuing fields of study in which they are unlikely to succeed. For  a big reason that, it is difficult to define what is success, which fields will be suitable for a student.Normally, students start to think about their carreer when they are going to college, when they have a lot chances to meet different people, touching all sorts of information. They want to be a successful person in their future, rich, healthy, happy or even a stable life. So here, different people may have different attitudes toward success. As  a instructor in college, he or she can not know a student thoroughly so that they are hard to give any definite suggestions.Morover, whether a student can success or not, depends on serveral factors, like knowledgeg, opportunity, thier interpersonal communication skills, etc. So we can not judge if he or she can succeed in the future career. For example, Jeremy Lin is a Chinese American basketball player who is famous at this time. But he is a undergraduate student from Havard University. We can never know what will happen on him. If one day, his teachers said to him to be concentrated on his major, and be a successful bussinessman in the next 5years, can he be a super star in NBA now? As life is moving all the time, amazing happens anywhere.As a good education, some one is responsbile for guiding and help the students to build up their own carrer, rather than lead them to a "better" way. Young people have a lot of chances to get to know the society, the surroundings and they will come up with ideas what they are doing to do. Some times when they about to start, they find it hard because of lacking resources or scant of knowledges, this is the right time the instructor should show up and direct students to tell them what should be a better idea, or is there any successful predecessor's experience, or something they need to learn to success.