it’s not even a secret anymore. Your rate of success is multiplied many times if you study and start your career in the field which intrinsically excites you. You cannot really be successful if you get bored easily. However, many people still continue making this unforgivable mistake of choosing career paths without considering their core interest
Don’t run for what is demanded in the market. Petroleum engineering, for example, may be the most demanded job skill in the world but it does not mean that there is no demand for good painters, good musicians or other type of engineers or doctors. You will always make your demand if you are exceptional in your skill set. And you can be exceptional in something only if you have interest in that.