spotz

My limited understanding is that the suit in question is avoided until the end so how would a defender show out of that suit? I guess I'm looking for an explanation that teaches how to make this kind of determination.

I've read a few Endplay examples which explain how to execute but none of the examples explain how to identify the opponent to be "thrown in". Is it just a guess that's only expected to work 50% of the time like a finesse? If you have a link to a resource on the topic, I'd be very interested in looking it up. Thanks