"More often than not" is an expression to say that an event "happens more often that it does not happen" (see https://english.stackexchange.com/a/187722/63461). How does one express the negative of this?
Less often than not?
More not often than often?
More un-often than ___?
Best Answer
Rarely, Seldom, or Occasionally in my view equate to something happening 'less often than it does not happen' as you put it.
They do however connote varying degrees of frequency, of which rarely seems the least often and occasionally somewhat more frequent.
Other similar phrases include... 'from time to time' 'every now and then' or just 'sometimes' ...would connote to me something happening less than 50% of the time
I don't think there is an exact opposite phrase of what you're looking for.
if you really need to be specific about something usually not happening you could just adjust the latter part of the sentence.
eg. "More often than not the birds fly away"
The opposite is "More often than not the birds don't fly away"
Depending on the sentence it could sound strange but is a potential solution.