Never trust.

When you hear your friend saying him/her not studying, then better IGNORE him/her.

They can tell you 1000 reasons of not studying but yet their result is much better than your. 

Or even they said they haven't finish their syllabus but their result still better than your.

So from now onwards, I'm learning how to say " no I didn't study at all" " no I haven't finish my syllabus" when anyone ask me whether have I prepared my exam.