How to prevent people from sharing their feedback? What would make people less honest and open?

• Ignoring the feedback you receive. If people think that their feedback is not going to change something, they won't bother giving it to you after a few tries.
• Not giving feedback yourself. The culture is shaped by the behavior of everyone on the team. If you don't provide feedback to others, it sets an example (this is especially true if people consider you a leader).
• Telling someone that they are exaggerating or are paranoid when they talk about a problem. It's a clear sign that their feedback is not important.
• Explaining why someone is wrong without trying to understand their perspective. It’s not about trying to convince the other person that you’re right. Even if you are, your goal should be first to understand their point of view.
• Stopping the discussions and arguments, calling them unproductive. That makes people question things they want to say. If someone has to think twice before saying something, there's a good chance they won't say it.
• Blaming others when you hear the negative feedback ("it's not my fault, it's …"), explaining yourself when you receive negative feedback.
• …

This exercise is an example of inversion thinking. Inversion is about thinking about the opposite of what you want.

Rather than thinking, "How to make people give more feedback?", think about things that prevent people from giving it. Then, make sure that you never do the things you listed. Giving feedback (especially negative feedback) is extremely hard! If you want to get more of it, make sure that you remove as many obstacles as possible.

One more closing thought. Despite what all the articles about the "feedback culture" say, receiving negative feedback will always be hard. Hearing about what you did wrong can be uncomfortable - even if it's good for you in the long run. Giving negative feedback is probably even harder. So don't be fooled by people claiming that by creating a "feedback culture", you can make any of it easy.

References

• Atomic Habits by James Clear is a fantastic resource on habits and human behavior in general. One of the book's claims is that if you want to change someone's (or yours) behavior, motivation doesn't work in the long run. What gets repeated is things that are easy to do. If you want more of something (here - feedback), remove as many blockers as possible and make it easier.
• Jessica Kerr wrote an excellent short article about the difference between motivating and enabling. If you want to see more of some behavior from a team member, think about how you can enable that behavior, instead of thinking about how to motivate that person.
• https://knowyourteam.com/blog/2018/10/18/the-2-things-that-hold-employees-back-from-giving-honest-feedback-at-work/ - This article shows that the two biggest reasons for not enough feedback at work are fear and a sense of futility.
• https://jamesclear.com/inversion - if you want to read more about inversion thinking