It is also hard to predict ones interview performance based on their personality, have heard very social people not getting offers and more quiet people getting spots.
Agreed. It is very hard to tell how you went in an MMI. I remember some of my friends said their MMI felt awkward and they still got in, others said they felt quite confident after their interview but they got rejected. There are many small things that come into play as well - such as body language and directness (ie actually answering the question asked, not the one you wanted to be asked, and not beating about the bush).
Although everyone should practise for their MMI, it is also very important to not come off as robotic or "rehearsed" (AND DO NOT LIE), just pretend the whole thing is a natural conversation rather than a high stakes exam.