Imagine that you receive a document. Unfortunately, this document has been chewed by a dog leaving various holes in the paper. Some of the holes are larger than others. Some pages are torn. All of them are damaged. You would be able to read much of the text, but there would be portions where you would find it difficult to fill in the blanks in the paper. This is the situation that scholars find themselves in when dealing with a fragmentary text.
Reading fragmentary manuscripts presents a challenge for scholars. Some lacunae are small and obliterate only a part of a letter. Most lacunae that only cover part of a letter create no problems for the reader. Sometimes, the lacuna will remove enough of a letter that more than one letter could be represented by the traces. Usually, though not always, in those cases one can determine the letter from the remaining letters of the word. Lacunae, however, might be extensive and leave whole lines or pages missing.
Sometimes a scholar can use his knowledge to reconstruct the text. The more extensive the text, the less likely that a scholar will be able to supply a possible text.