Why do some people earn so much money until they don't know what to spend on, yet some people have to scrimp and save to make ends meet?

It's like heaven and hell.

The rich makes more and more each time.
The poor scrimps and saves like mad.

But then again, top 5% of Singaporeans are making at least 5k a month. That leaves many others who earn below that not very far either.

Some work so hard to get that 5k per month.
Yet some can eat, drink, party all day with money rolling in more than 10k per month.

What's the secret behind these?