Listen to dissenting voices
Sam tells that during the course of developing a set, some people are going to encourage you. Others are going to criticize or tell that they are not happy with this or that. A game developer will naturally focus on the good things, not wanting to hear the bad things. What he has learned over time is that people who say that they are unhappy with a card or the whole set are not wrong. They can be, but you can't just ignore them or try to prove that they are wrong and you are right. If during playtest one or more people were not happy, chances are that people from your target audience are going to say the same thing and complain about the same issues. They can't please everybody at the same time, but they must try to please the widest possible audience. As Mark Rosewater states, for every card that is loved, somebody else is going to hate it and vice-versa.
I gotta say that this is closely related to ego. People who cannot stand being criticized, even if positively, have fragile egos. In extreme cases we have a mental disorder. We have two extreme opposites here: people who are unable to say no and people who say no to pretty much everyone. In the case of game design or level design, if you are unable to say no, how are you going to get your own ideas in? You'll never be able to be pro-active by always saying yes (accepting either passively or actively). In the other extreme, if you deny everyone's opinions and stick to yourself till the end. How are you going to collaborate or even accept collaboration then? Unfortunately I don't have an answer for this. I'd say that if you can at least hear them and compare it against your beliefs and ideals, at least you have made the effort to listen and process it. One of the most challenging issues with all personality disorders is that these people have a very limited capability of listening and processing it.
What Sam says about listening to dissenting voices is very much the same discussion that we have in society itself about prejudice, racism, sexism and so on. Within a game development company we put ourselves at risk if we deliberately choose to silence those voices or ignore them. I think that Sam's lesson is that dissenting voices are a good thing because we ultimately need them to point out the unfairness, unhappiness, dissatisfaction, that they are seeing but we are not.
I'd add something that is more personal than a real wisdom. If you hate what you do, chances are that your target audience is going to see it. Regardless of how much effort you make to try to conceal that hatred. In the case of level design, if I were to hate a certain level which I'd be working on. I wouldn't make an investment to make it the best level possible. It just wouldn't work.
