The article goes into the three reasons that a leveraged ETF may underperform its multiple of whatever it's tracking. The fees are generally close to 1% although they're getting less over time and certain funds like NTSX have fees that are down around 0.2. Another potential problem is tracking error that however they've constructed the leveragedETF it does not accurately track the index that it's supposed to be tracking. And the third one is called volatility drag which has to do with the fact that since they are much more volatile over long periods of time you have the same issue with looking at the arithmetic mean of say the S&P 500.