Don't mistake luck for skill.

One must invest but that doesn't mean that your past successes will determine your future successes. Holding cash is a risk averse strategy and you may do well compared to the tons of people who don't invest but also don't have cash (yes, many of them exist). However if your strategy is compared to an aggressive one, then your future returns may not be as impressive.

In the end, it's mostly luck.

If not, GIC and Temasek would have been much more successful.