A long time ago on an island far away... called Nauru, they tried to invest their wealth from their natural riches (phospor fertilizer). It didnt work out, if I remember correctly.

It's a strategy that's worked well for Norway though

Doesnt Norway still produce oil? Naurus strategy also worked well as long as they were producing. (Although I am not worried about Norway, even if the investment were not to work out as intented, their economy seems sound)

However Norway was already one of the richest countries in the world before the oil boom. So there wasn't as much pressure on their government to spend that income immediately instead of investing it.

Its also worth considering that Norway has a highly educated, intelligent population and an open, protestant culture. Countries without these traditions or a less educated population are more prone to corruption and mismanagement.

Is that investment just finding a place to park money? Or does it do something good for the every day Saudi citizen? I don't follow the issue closely enough to know.

Following the list of Softbank "successes" seems like a decent proxy.