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Defensibility Fallacy

26 November

We’ve all heard about the “sunk cost fallacy”, “bike-shedding”, and the “mythical man-month”, but I’m here to introduce you to the “defensibility fallacy”. 


The scene:

Monday, and it’s already been a looooong day, and it’s only 10:30 in the morning, but you’re working from home so that’s nice, except there’s this pandemic and remote collaboration tools are frustrating thanks to Microsoft’s consistently-not-quite-acceptable-but-you-have-to-use-it-anyway UX.  You’re being tasked with taking a look at one maybe even two or three technologies/libraries/products and make note of the various pros and cons, keeping an eye out for showstoppers, non-starters, gotchas, and whatever. 

This time, you’re happy to - there’s this tech that does a thing called “arbitrary feature that’s actually a real thing and is very powerful” (umm, let’s just call it [arbitrary feature]) that I saw a talk about.  It’s cool, trust me. 

You do your due diligence and prepare to present your pros and cons. 

Pros of new coolness

  • It has [arbitrary feature]
  • … other stuff


Pros of alternative

  • Under certain circumstances there is a minimal but continual benefit that’s kinda hard to explain and definitely hard to quantify. 
  • … other stuff

So what happens next? 

Well, the defensibility fallacy starts influencing conversations.  Nobody wants to be the moron suggesting we forgo [arbitrary feature] in favor of a hard-to-explain hard-to-quantify benefit.  I just woke up and you want me to find the words to explain why it might be better to do the hard-to-quantify thing?  “Why don’t we just go with the one with [arbitrary feature] and see where it takes us?”  “Others in the industry seem to be doing [arbitrary feature] things.”  Buzzwords pop in and sure enough, the “defensible” option wins. 

Its influence can be lessened. 

First, make sure you’ve done a thorough job collecting pros and cons. 

Second, present pros and cons with equivalently complex language and mental models.  Give catchy & relevant names/words/phrases to things so they can be easily referenced in conversation. 

Third, ensure you’ve quantified what can be quantified and qualified concisely the rest.