A look at some examples of finesses that are not quite straight forward.
The links to the hands are:

With 8 cards, finesse against the Dangerous Opponent: http://tinyurl.com/y6ukhv5z

With 9 cards, finesse against the Dangerous Opponent, rather than risk cashing AK http://tinyurl.com/y8mvopc5 POLL1 How to play the Clubs : Cash AK, or finesse?

Even if the finesse fails, you will make 10 tricks http://tinyurl.com/ydax2a8k

On this hand East is the dangerous opponent – you must prevent him gaining the lead, as a diamond from East will defeat the contract http://tinyurl.com/ya9gdsor

If the finesse loses, West cannot attack diamonds, without giving you another diamond trick http://tinyurl.com/y8rdayme

You must play the diamonds in such a way to prevent East from gaining the lead. Only if East has QJx will she regain the lead http://tinyurl.com/y9ejzg3g OMIT from this lesson

You may lose the lead to KD and to AH – you should play Hearts first – Lose to the dangerous opponent first. You can only lose KD to the less dangerous opponent.

POLL 3 which suit should you play first? https://tinyurl.com/46r5efct - wrong
https://tinyurl.com/25dm6lba - correct

Repeat Finesse and entries
You have 7 top tricks and hope to make 2 more in hearts https://tinyurl.com/2ycfedna If you start by leading 9H you may not be able to repeat the finesse
https://tinyurl.com/2b88un7y

Instead start by leading a low heart https://tinyurl.com/46r5efct