Which Sith must not believe, unless they are just flat-out stupid. Palps seems far too cagey to adopt a philosophy that he knows will destroy him in the end - what's the advantage of that? Maybe if Palps were one of those people who just can't think long-term, but if there's one thing he excels at, it's long-term planning.
Well, I wouldn't say it's guarenteed to destroy you but you have to be on guard so that it doesn't destroy you.
If we've learned anything from the movies, it's that Palpatine is a massive long-term thinker. The way he rose from Senator to Chancellor to Emperor, how he manipulated events and worked on turning Anakin for more than a decade, this guy is the master of the long-term plan. If Palpatine had a flaw in the end, it was that he wasn't as good of a military planner as he was a political planner. He completely underestimated the Rebels and Ewoks at Endor and he was so confident in himself and the dark side that he thought Vader would do nothing as his son was tortured. It bit him in the ass.
In fairness, it's easy to see why Palpatine got so overconfident. He had succeeded big-time in the prequels. He decided to work his old and very successful formula in ROTJ (lure the Rebels into a trap by thinking they have secretly obtained the Death Star plans) and in the end, it backfired dramatically.