Short quotations with their attribution attached, and where the attribution is disputed, the tool says so rather than inventing certainty.
Most quotation collections online are wrong about who said what. Lines drift toward famous names because a striking sentence attributed to Einstein or Twain spreads faster than the same sentence attributed to someone you have not heard of, and once a misattribution is circulating it gets copied between sites indefinitely. The set here is small and each line carries its attribution, with the disputed ones marked as attributed to rather than presented as certain. That is less satisfying than a confident credit and considerably more accurate.
A quotation works when it is doing something the surrounding text cannot do alone, compressing an argument, or lending an idea a voice with more authority than yours. It fails when it is decoration, which is what most opening-slide quotations are. Keep it short, credit it properly, and if the attribution is uncertain say so rather than picking the more impressive name. If you are quoting at length rather than a single line, check the copyright status: short attributed quotations are generally fine, extended passages from work still in copyright are not.
Because the attribution is disputed. Marking it is more honest than picking the famous name, which is how most misattributions spread in the first place.
Short attributed quotations are generally acceptable, but rules vary by jurisdiction and use. Check the status of anything still in copyright before printing it.
Because every line has been checked for attribution. A larger list would mean including quotations whose sourcing could not be confirmed.