I'm trying to understand what makes a person's ba zi wealthy and successful. Donald Trump and Steve Jobs have no DW but is really rich and successful, how come?

Who says DW must be their wealth stars?

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Cheers.

 Peter, is it because Trump has a Weak Day master, therefore his wealth stars are actually Rob Wealth, Friends and Resources? He has a lot of this on his Bazi. 

Another question, how do we know if we have a Strong day master or not?

They are extreme strong 专 which share the same favorability as weak self.

Some are easy to determine their self’s strength but others can be quite complicated. Don't be fooled when someone told you that once you were born in season you are strong. Born in season is only one of the many conditions. BaZi courses

Cheers.

For a Weak Day Master, is it even true that without any DW or IW in their chart, it means they will have to work hard for their money? 

Weak self does not need DW or IW to get rich. When DW too strong it will do a lot of harm in term of money.

Cheers.

 Sorry Peter, let me rephrase my question because it wasn't clear.

If a person's Day Master is Weak, and they lack DW/IW in their chart, does that mean they have to Work Hard for their Money? 

It depends on how strong and how healthy is his 比 Bi-jian Friend, 劫 Jie-cai Rob Wealth and whether 比 Bi-jian Friend, 劫 Jie-cai Rob Wealth his wealth stars have protections or not.  When strong, healthy and protected no need to work hard and money will knock at your door. And this depend on many other criterias to consider for example their elements, where are all these stars Ten Gods 十神 located in his BaZi, TaYun and years, suppressions, productions, combinatiosn, transformations etc.

Instead of asking whether you have DW/IW, you should find out whether your wealth star (比 Bi-jian Friend, 劫 Jie-cai Rob Wealth for weak self) is strong, healthy and protected. These DW/IW, Output, DO so on all contribute to this  “strong, healthy and protected”.

Cheers.