"Sobering fact" means that something is a reality or piece of information that makes you serious, thoughtful, or sad because it is serious or unexpected. Full definition
It is sober fact in the light of which all life is most realistically to be lived. (religion-online.org)
Protect Our Winters, an environmental advocacy group, accompanied the athletes and presented sobering facts about the economics of the industry: Low snow years have caused the loss of 17,400 jobs and decreased the estimated value to the economy by over $ 1 billion since 2001. (mindbodygreen.com)
One of the most sobering facts of bodybuilding is that muscle growth is not an infinite process. (fitnessandpower.com)