Leave room for the player to explore

The players enjoy to discover things. In Magic there is an uncountable number of card's combinations. Mark cites two cards that are not meant to form a combo, but they do. One is a blue card that copies every instant or sorcery, granting copies to all other players when a player casts one. The other is a green spell that costs zero and searches its owner's library for a creature. The caveat is that it costs zero, but the next turn the player is forced to pay a cost to not lose the game. When both cards are combined they create a new situation in which players are forced to do something, else they lose the game. In magic, when a spell is copied, all properties of it are copied, including the extra costs.

Mark has worked as a script writer for TV and one of the lessons he had was how to talk with your audience. It's so important to talk with your audience that in Hollywood people take classes to learn it. The trick that he learned is that you have to talk with your audience, invite them to talk with you, not to tell a story and expect them to listen and do nothing else. The key is to pitch, tell part of your script and invite the audience to take part in your talk and ask questions. This makes the audience more activate and more likely to buy your idea. It's a way to evoke the audience's curiosity, otherwise they wouldn't be invested in your story and would be less likely to buy it.

Addendum: in regards to psychology there are two things that I've read that are important to highlight. Some people tell a story and expect everyone to listen to it and not question anything. This is one of the characteristics that define the narcissistic personality. There are also people who become so immersed in their own storytelling that they disregard what others are thinking or experiencing while they are telling a story, which is a sign of egocentrism or a lack of self-awareness. Whatever the case is, from the perspective of developers and designers I think that we often want to impress the player and to do so we inadvertently attempt to impose our views onto the player without questioning whether the player is happy with it or not.

In terms of level design this means that people will be more invested in games that allow players to explore and find secrets. Designers can feel the need to show and tell everything in one go. However, when the player have the opportunity to explore and discover without feeling forced to do it, the player is more like to invest himself in the game.

The most basic form to invite the player to explore is to leave secrets in levels. Doom did that in 1993. Bioshock did that. Alan Wake did it too. Many games come with cinematic sequences that the player can only watch and not interact with. Some games such as Uncharted allow the player to interact with cinematics but that is a technical challenge as the level design, scripting, all have to be made in way that doesn't allow the player to inadvertently break it. The worst case scenario is the player being unable to progress any further due to some unexpected behavior.