Suppose you are trying to create a list. It may be of the "best" popular science books, or most controversial movies of the last twenty years, tips for getting over a breakup or the most interesting cat gifs posted in the last few days.

There are many reasons for wanting to create one of these lists, but only a few main simple methods:

1. Voting model - This is the simplest model, but popularity doesn't always equal quality. It is also particularly problematic for regularly updated lists (like Reddit), where a constantly changing audience can result in large amounts of duplicate content and where easily consumable content has an advantage.
2. Curator model - A single expect can often do an admirable job of collecting high-quality content, but this is subject to their own personal biases. It is also effort intensive to evaluate different curators to see if they have done a good job.
3. Voting model with (content) rules - This can cut out the irrelevant or sugary content that is often upvoted, but creating good rules is hard. Often there is no objective line between high and low-quality content. These rules can often result in conflict.
4. Voting model with sections - This is a solution to some of the limitations of 1 and 3. Instead of declaring some things off-topic outright, they can be thrown into their own section. This is the optimal solution, but is usually neglected.
5. Voting model with selection - This covers any model where only certain people are allowed to vote. Sometimes selection is extraordinarily rigorous, however, it can still be very effective when it isn't. As an example, Metafilter charges a $5 one-time only fee and that is sufficient to keep the quality high.