I think it just means being open to the possibility that things can be perceived differently at different times for valid reasons. There is always the spectre of the undefinable "other". I like this late comment from James Lovelock too.
"One thing that being a scientist has taught me is that you can never be certain about anything. You never know the truth. You can only approach it and hope to get a bit nearer to it each time. You iterate towards the truth. You don’t know it."