Don't praise the participant's performance
When facilitating a usability session...
DO: "You are doing a great job at narrating your thinking."
DON'T: "Correct. You completed the task."
DON'T: "Yes, perfect! Very good. You guessed right."
The latter two examples reward the participant for succeeding with the product. This implicitly tells them that we want them to succeed - we don't want them to struggle.
Participants will sense this unsaid expectation and they will try to be that. What's worse, they will try to cover up their failures. How this manifests is:
- they will try to hide their frustration, they will try to hide their confusion because confusion means they are not acing the tasks.
- they will do less think aloud - they will only talk to you when they already have the answers. They won't let you in on their struggle that happens before that.
Ultimately you will end up with much fewer usability results.
The participants' job in usability sessions is NOT to succeed on the tasks and you shouldn't imply that. The participants' job is to let you in on their thinking while they are doing the tasks, so you may spot their struggles and confusion.
If you must praise the participant (e.g. because they are feeling insecure and need some friendly encouragement), praise their effort at narrating their thinking. "That's good thinking aloud.", "Yes, that's exactly what I want: to hear your thinking process as you are working your way through..."
Does this resonate with you? Do you have a different perspective? Let me know in the discussion below.