The phrase "unavoidable fact" means something that cannot be escaped or prevented. It describes a truth or reality that is certain to happen and cannot be changed. Full definition
As the saying goes, there are two unavoidable facts of life: death, and taxes. (sparxtrading.com)
When we started, the conventional wisdom was that killing homeless pets was an unfortunate but unavoidable fact of life. (la.bestfriends.org)
The scale and physical eccentricity of the work do not take well to wainscoting and other unavoidable facts of the academy's busy Beaux - Arts interior. (nytimes.com)