No, all people are not selected. JEE is not difficult, it is tricky in its approach. The questions asked in the exams cannot be answered by plane mugging up of textual concepts. JEE questions, test deep and clear understanding of the concept.
The reason JEE question paper is designed this way is to check if the candidate has true passion and understanding of engineering before they join the best engineering and technology universities in the country.
Another reason why students dread IIT-JEE is that today thousands of coaching classes for IIT-JEE has popped up all around the country. This perhaps creates an impression that an examination that requires coaching at such a level must be difficult.
As every question carries equal weightage, the candidate should be smart enough to understand the question he/she will be able to solve easily and dedicate more time on those questions. This way, the chances of a better score increase substantially. The student must understand that given ample amount of time, every aspirant can solve all the questions correctly. The trick is in scoring the maximum in the given amount of time.
All said and done JEE does require an ample amount of hard work. There is absolutely no substitute for that. Only with a good amount of practice, can a student get complete understanding and clarity about the subject. In an applicative competitive examination like IIT-JEE, only hard work, rather smart work can guarantee desired results.