IContact vs Contact difference/best practice

Summary

Trying to understand when to use which object

Content

This one has tripped me up on a number of occasions and I go down a rabbit hole every time I run into this blocker. I'm trying to understand when you would use I<Object> vs just <Object> It seems like the methods available and even the attributes available to each of these objects change based on cast. You can't cast back and forth between them, so I always end up having a problem where I need to hit an attribute of an i<object> that isn't as clearly exposed, or i need to iterate through an <object> which doesn't have iterable