I grew up in a small village and hadn't heard of JEE before I entered the 12th grade. I tried to prepare by myself and failed spectacularly. A lot of the questions rely on tricks or insights that you typically learn only in coaching classes. My neighbor's son, who actually went to school in a nearby big town, had signed up for coaching classes. He did much better than me, and from chatting with him (post-exam), I could tell he had learned these tricks in his coaching classes.

So, clearly, lack of coaching classes hurt my chances.

In any case, I never joined the IITs, but joined another engineering college thanks to my scoring very well in the final exam.