Amplifying the lizard brain
Not sure why you would want to reinforce the noise in your head that tells you not to speak up, stand out and do work that matters, but if you do, a surefire way to do it is to focus your attention on every piece of negative feedback in your environment. Or to imagine every possible disaster that could befall you, and to do it repeatedly. Or to carefully study anonymous comments, tweets and online reviews from people who don't like the work you're doing. Or focus on the one paragraph in your annual review called 'weaknesses'. Or spend the day thinking about the one slip of the tongue you made this morning...
You can listen to your customers murmur about you online, except that pleased customers tell a few people, angry ones tell everyone. So it's really easy to misinterpret a few as a deluge.
On the other hand, once you accept that this is self-sabotaging behavior, you might choose to deliberately ignore interactions that amplify the very noise you're trying to avoid.