Continuously? Ok, perhaps that would be almost impossible, to pull off 20% for 20 years without missing a year.

However, Buffett and Soros managed to average above 20% annual returns over 30 plus years.

For example in the 1960s Berkshire returned 28.3% per year averaged. In the 1970s it returned 22.2% per year averaged. In the 1980s it averaged 39.1% (!) per year. In the 1990s it averaged 20.5% per year.

Nobody would hold their breath on another investor matching Buffett or Soros. It is in fact possible though. The big problem for the Norway fund is obviously the scale. Berkshire at $360b in market cap, will struggle perpetually going forward with keeping up with the S&P 500 over time (as is frequently noted by Buffett).