Selfishness is a rather interesting trait inherent in almost every person. Just to some more, and to some to a lesser extent. And the levels of selfishness can also be different.
For example, many people, thanks to selfishness, achieve success in their studies or career advancement. If people thought about others more often than about themselves, few would have achieved such success in an honest way. Honesty is not always a good quality, sometimes it can ruin a career or financial situation.
Sometimes a person only cares about himself, but there is a category of people who are used to taking care of someone from their relatives. However, such concern is also most often accompanied by ignorance of the interests of other people. For example, when buying an expensive foreign car for a daughter or wife, many simply forget that someone before them could want to buy this car. And there are infinitely many such examples.
But also too soft a character is only harmful to the person who is endowed with it. After all, if you do not know how to refuse help to strangers or relatives, then, in the end, there is a chance that either one or the other will sit on your neck. And this will further undermine the self-confidence of such a weak person. Therefore, you need to reconsider your life priorities.
Selfishness should not be the predominant feature, however, it is necessary to clearly understand that a smaller part of the subconscious should be responsible for it. It is possible and necessary to reckon with the opinion of others, but not to the detriment of one's own interests. Most often, for success in personal life, study or work, a person should thank, first of all, himself. Selfishness has more than once helped many great scientists to reach certain heights in their careers or make this or that discovery. They did their job contrary to what they might think of them and not following anyone's advice and, in the end, they did succeed.
If the degree of selfishness is too high, you just need to reconsider your qualities and change for the better, having studied the basics of personality psychology. You can conduct special trainings, for example, by standing in the place of someone whose opinion was once not listened to or who stepped over to achieve their goals. Then compare the sensations. And continue to prevent such disagreements, or to minimize.
Selfishness can be both harmful and beneficial. It all depends on the person and on the attitude towards others, as well as on those qualities that were laid down from childhood. Therefore, before developing such a quality in yourself to achieve success, it is worth looking for other ways to solve problems.