From Imperial Wiki
The Light Side of the Force is an aspect of the Force that can be manipulated through mental discipline. The Light Side is considered to be a slower and more difficult path to mastery of the Force, but it tends to be more reliable, since the Dark Side sometimes betrays its users unexpectedly. Light Side practitioners tend to be selfless compared to Dark Side practitioners, and they are generally unwilling to use the Force as a weapon against living adversaries.
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