A common misconception is that a ||= b is equivalent to a = a || b, but it behaves like a || a = b
In a = a || b, a is set to something by the statement on every run, whereas with a || a = b, a is only set if a is logically false (i.e. if it's nil or false) because || is 'short circuiting'. That is, if the left hand side of the || comparison is true, there's no need to check the right hand side.
For more information, please refer to explaination below:
What Ruby’s ||= (Double Pipe / Or Equals) Really Does