What is meant by the phrase "what is generally afflicted by tribulation"?

"ʿUmūm al-balwā" refers to widespread matters that are difficult to guard against, such as a small amount of blood, pigeon feathers in the mosque, a torn garment when sitting next to its owner in the mosque, and pictures and writings on widespread packaging and papers. This principle is based on the Almighty’s saying: (And He has not placed upon you in religion any difficulty), and (And He has already explained to you what He has forbidden to you, except what you are compelled to [eat or do]), as well as the Prophet’s (peace be upon him) narration about the cat, and the rule "Difficulty brings ease."