"If you have two theories that both explain the observed facts, then you should use the simplest until more evidence comes along"

"The simplest explanation for some phenomenon is more likely to be accurate than more complicated explanations."

"If you have two equally likely solutions to a problem, choose the simplest."

"The explanation requiring the fewest assumptions is most likely to be correct."

. . .or in the only form that takes its own advice. . .
"Keep things simple!"