Single career or several careers? Both have negatives and positives

Present a written argument or case to an educated reader with no specialist knowledge of the following topic:
The idea of having a single career is becoming an old fashioned one. The new fashion will be to have several careers or ways of earning money and further education will be something that continues throughout life.

Having single career or several careers is a case with many issues, which has both negative and positive aspects. Also, to be able to have several careers or to be promoted to a higher position at work, a person has to hold qualifications higher than a diploma or a bachelor degree. There fore, he or she has to attend classes for the rest of the life as education never ends.

In my opinion, attending classes while working is very tiresome because as a full-time worker, a person has to attend part-time classes like, classes at night, to achieve a specific qualification certificate. The person does not has time to rest as he has to go to classes after work, then come back home with piles of office works and lessons. Even on Sundays, he might has classes to attend. So, it appears that there won't be relaxation time for him. As a matter of fact, if he is not a person with strong spirit, he will definitely give up all he is trying and fighting. It is even worse if he is a money chaser with several career. Actually, this could even put him into madness.

However, there are always ways to solve problems. I believe that, although having several careers is good in some ways, this could drive a person crazy. Because he will has so much pressure. Therefore, the solution is to emphasise on one career and compete to get to a higher rank. The higher the position at work, the more money you are going to make. But you may indeed have to chase education to achieve promotion requirements, for example, to become a CEO, you have to have MBA degree.

Of course there are people who could deal with several careers plus further education but only a few make it throughly. Therefore, justify yourself, whether you can handle tons of works or you just want to go up slowly and steadily. Everything will benefit you in the long term.

I see a couple of problems here. First, there's no clear thesis. You just ramble on about various aspects of having multiple careers, not even fully addressing the question of the prompt.

Next, your sentences are sometimes so wordy as to inhibit understanding. For example:
Having single career or several careers is a case with many issues, which has both negative and positive aspects.
What does "a case with many issues" mean? How is "having single career or several careers" a "case" anyway? I think maybe you are simply trying to say that having multiple careers rather than a single career has both positive and negative aspects, but that gets lost in the jumble.

Moreover, it sounds like the prompt wants you to explain why having multiple jobs is becoming the new norm, thereby demonstrating your awareness of the factors that contribute to that trend, and then go on to explain what that trend means for individuals.

Oh! I now see my mistakes.
Thank you very much Simone.
:)

You seem to be arguing that having a single career is easier than having multiple ones. However, Simone is right -- the prompt seems more to be asking you to explain if the trend exists, rather than if it is good or bad. You can certainly mention both the positive and negative social and psychological aspects of this trend, but at the moment the first half of your essay seems to be missing.