There could be a number of reason why, sadly, these people don't contribute to discussion. Maybe they just aren't very good at it (I'm not particularly but I always like to have a go) and feel a tad embarrassed by it. Or perhaps they just like to read these posts out of interest. Or maybe they feel it's not their place to contribute for one reason or another or just don't know what to say. I used to be one of these people who would read stuff and not contribute because I felt that, if I said anything, others wouldn't find what I say relevant or stupid. I'm glad that I no longer feel like this.
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The only person in the world that can truly make you happy is yourself.