Using ifFalse: instead of ifTrue: as a guard clause

Smalltalk by Example advocates returning using an ifFalse test that returns self rather than an ifTrue test that then executes your code. For example doing this:

MyClass>>someMethod
 (some condition) ifFalse: [^self]
 self doThingOne.
 self doThingTwo.
 self doMoreLinesOfCode] 

instead of:

MyClass>>someMethod
 (some condition) ifTrue:
  [self doThingOne.
  self doThingTwo.
  self doMoreLinesOfCode]

I don't think I understand this properly yet. There is something odd about asking, for example a list to do something, and for the return result to be the list. I am not sure how my coding would cope with that, i.e. rather than getting a failure message or something like that. More pondering required.