Hello, Yes it is very possible for JEE-MAINS. If you search around you can find so many students who have prepared for JEE-MAINS without joining any coaching institute. But joining a coaching institute has its own advantages like coachings provides precise study material for preparation and reputed coaching institutes have very evolved teaching techniques and they provides you good mentors. These mentors will give you many tips and tricks related to the topics, formulas which will eventually help you in your revisioning process and will reduce the question-solving time(which matters a lot in such exams). Plus good mentors clears your doubt on the spot and keeps you motivated throughout the preparation. Like anything else you may come across such situations when you will feel de-motivated you'll think that I can not take it to the end and a lot of other negative thoughts and here a good teacher/mentor plays a significant role by not letting you yourself down.