In my current project team, I try to encourage an open atmosphere and discussions. In general, I have the impression that we are on a good road in that regard.
The idea of a post-mortem after each iteration was well received, except for one colleague who refuses to express opinion when asked for the first time. Common responses might include "I may not say" or "this is not important now". I think it is important to add that I experience him as quite introverted a person in general, and that this might simply reflect his personality. At the same time, I'm very convinced that actually he is willing to improve things, and that he does have something to say. Several times I got quite constructive responses already, once I was pushing (i.e., 'Indeed I do think it is important, please share your thoughts' or something like that).
I'm wondering what makes him feel so uncomfortable about openly telling what he thinks right away. I really hope I've demonstrated several times already that there is nothing bad to be expected from honest and constructive feedback.
Maybe he also thinks that entire discussion is for naught. However, from my point of view they are the best way of discussing what went wrong this time and thus improving in the future.
This way or the other, the key question is: Should I insist on getting some feedback, with the best intention of improving something both for him, the rest of the team and the client, or rather accept that somebody is not willing to share his thoughts?
Of course, I could never avoid that anybody just says 'all fine for me', but I strongly feel that once somebody expresses that he has something to say, he also should do so instead of holding back.