The underlying and abstract thought behind the simple idea of making games 'fun'. Simple to understand, hard to master. Anybody can write up a design document with countless revolutionary, inventive, and well-documented ideas. It is only a true Design Theorist who can make that design document produce a fun and addictive game.
A Lossy Compression, used in such formats at .MP3, discards what it feels is 'unnecessary' information during encoding. Therefore, after compressing a file with a Lossy format, you are unable to decompress it to the same state in which it was originally. While many times this information truly is unnecessary, proponents of lossless compression would argue that it's a sloppy practice.
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