"The simplest explanation (the one that makes fewest assumptions, and posits the fewest entities) is the one that should be preferred"
"The explanation that you believe is correct will always seem simplest to you."
Yes, this is partly joking -- but there's a serious side to Adam's Razor: the measure of the number of assumptions or entities depends on your beliefs. You might be tempted to overlook your core beliefs when assessing the assumptions on which a statement depends.
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Wikipedia: Occam's razor