There is a popular analogy today that refers to "the elephant in the living room". This phrase is an amusing way to talk about a very serious matter, un-discussable team issues. What makes an issue un-discussable is anyone's guess. It could be that the unmentioned issue will create embarrassment for someone, might surface unwanted conflict, or is simply a topic that team members don't know how to broach.
Much like an elephant in the living room, the unmentionable issue gets harder to ignore over time. The longer it goes unattended, the messier and larger it gets. It eventually interferes with team functioning like an elephant in one's living room would hinder a normal lifestyle. Although the issue is never directly confronted, it takes team energy and focus away from the job, and preoccupies the team with a disruptive distraction.
As you might suspect, to move the elephant out of the team living room you must deal with it. The first step in doing so is to acknowledge that it exists. This means that someone on the team must be brave enough to bring up the issue and accept the consequences involved with shedding light on the subject. The person who does so should be ready to hear others deny that the issue is real, and that it has relevance to team functioning. Despite these protests, the party who sees the issue must be able to provide tangible evidence that the undisclosed topic is indeed pertinent to team success.
It is necessary to remember that un-discussable issues remain so because they pose a threat to something or someone that the team values. Be as discreet, kind, factual, and non-judgmental as possible when surfacing the issue and you will increase the likelihood that the topic will be addressed rather than swiftly swept under the carpet again.