(image by puc87 on DeviantArt)
Muses come in many shapes and colours. Being an artist includes the ability to recognize a good Muse from a bad one. A Muse is almost never bad from the start, but it can grow weaker in time. On some days, the Muse sprinkles the magic fairy dust that makes you fly right into your brain cells (different Muses like different routes of administration), and if he or she are not properly trained, they will take leaves and go missing for long periods of time, sometimes without notice.
Basically, Muses can be flaky.

