You make a good point, but a distinction should be made between fleeting (intrusive) thoughts (like you meet someone and want to punch him for no reason, or yell fire in a theater for no reason) and things you really think, but don't say. Like that you don't like marzipan, which your in-laws think you like.
In some cultures (e.g. some European countries) people are very frank with each other, and that sometimes helps to clear up miscommunications more quickly.
What I dislike is people who praise themselves a lot. It might be true, but I was brought up to be modest, and I feel at a disadvantage when I am with people who toot their own horn a lot. And it annoys me.
Yeah, the distinction between fleeting, intrusive thoughts and ongoing things you're afraid to mention is important. The important thing about things like telling your in-laws you don't like marzipan though is that these are the sorts of things that you should really think about before you bring them up. They aren't the sorts of things you should just voice as they come to mind... the sort of honesty this article is talking about seems to imply the thing to do is to tell your in-laws how much you hate marzipan the moment you think it in their presence which would probably be the moment they give you some. It's probably a better idea to reflect on the goodwill they're expressing toward you and formulate an appropriate response before saying anything. The difference between voicing a gut reaction like "You know, I hate marzipan" while they're handing it to you and saying something like "I appreciate the gesture but I really can't stand marzipan" is huge.
Modesty, as you mention, is also a great example. There's nothing wrong with mentioning the things you've accomplished when it's relevant but it's important to know the time and place for it. You might talk about your skills and successes in a job interview for instance as it's the proper time for it but if you go on like that when you're with your friends you'll probably get tiresome.
In some cultures (e.g. some European countries) people are very frank with each other, and that sometimes helps to clear up miscommunications more quickly.
What I dislike is people who praise themselves a lot. It might be true, but I was brought up to be modest, and I feel at a disadvantage when I am with people who toot their own horn a lot. And it annoys me.