Books, Music, Podcasts, What's on the Design Wall

The “Planning Fallacy”

Continuing my latest binge of nonfiction self improvement audiobooks, I am currently listening to Nudge: Improving Decisions About Health, Wealth, and Happiness by Richard H. Thaler and Cass R. Sunstein.

Image credit:

In this book the authors discuss the concept of a “Planning Fallacy” in their section on “cognitive bias”. 

Wikipedia defines a planning fallacy as “a phenomenon in which predictions about how much time will be needed to complete a future task display an optimism bias and underestimate the time needed.”

Well, I recently made quite the “planning fallacy” in relation to the pillow top I’ve been working on (and discussed in the post Pillow Popping with the Untethered Soul).

Using 2.5″ x 2.5″ scrap squares, I made an endless batch of half-square triangles (HSTs) to create a pillow top based on a pattern from the book Pillow Pop: 25 Quick-Sew Projects to Brighten Your Space by Heather Bostic.

I assembled the HSTs into this layout:


I thought I could sew all the half-square triangles together in an afternoon, no problem. Not just one pillow, I thought I might get a second pillow top done too (as I had a zillion HSTs).

However, as I began to sew them together, the pillow top started to significantly shrink and I had to add on more and more rows of HSTs to make the pillow top large enough for my intended pillow form:


This photo illustrates the difference of how wide I thought the pillow top would be compared to reality:


How my planning fallacy occurred: Based on the original pattern I thought I only needed 50 HSTs per pillow and I had nearly 200 HSTs – so I thought I could make FOUR pillow tops! However I discovered I needed like 196 HSTs for just ONE pillow and I spent most of the time I planned for sewing the HSTs together, to add on MANY more HSTs to make the pillow top wide enough.

What happened during my original planning? Well I never paid attention to the size of the original squares to create the HSTs in the original pattern (much larger than the squares I used, and if I was motivated I would get up from the sofa, find the book and give you the actual dimensions…).

As you can see from the photo above, I have half the pillow top pieced and I cannot believe how long it took me to just get half a pillow sewn together!

I will only be making ONE of these pillows. Next time I work with HSTs and a pattern, I will pay more attention and do better planning!


On a more pleasant note, my lilac bush/tree is full bloom and my backyard smells wonderful!


During an intense Spring weeding session in my backyard this weekend, I paused for a “lilac break” and stood in front of the lilac bush and inhaled the incredible fragrance.

The scent of lilacs reminds me of being in my grandmother’s backyard in Pennsylvania as a young child. Lilacs smell like sweet childhood memories.

37 thoughts on “The “Planning Fallacy””

  1. I aim to plan stuff all the time – it rarely works out, ha ha! I have been in a similar situation with patchwork piecing – it’s all about planning in the seam allowance. Of course I know that (you known that too of course) but if we didn’t make little errors like this we wouldn’t be human. I love your pillow top, great selection of fabrics.

    Liked by 1 person

    1. Thanks so much for your insightful comments – you are so right – these issues keep us human 🙂
      So until robots take over and make all the crafts (ha) then we’ll just keep having our little “planning fallacies” but still creating!

      Liked by 1 person

    1. Yes it is a great bias to have otherwise we might just give up on crafting all together (part of me wanted to rip all the HSTs off the design wall and move onto something else but I did not). Thanks for your comments 🙂

      Liked by 1 person

  2. So true, I thought I’d just whip the tap off my shower and change the washer and it shouldn’t take more than half an hour. 3 hours later and old washer is still in there. It’s been in there 20 years and its decided it won’t budge 🙂 It’s a lot more fun when my sewing doesn’t go as planned.

    Liked by 2 people

    1. Oh no – sorry to hear of your shower repair fiasco! I agree a sewing planning fallacy sounds much more fun than a home repair planning fallacy 🙂


  3. I love this! A “planning fallacy” is the perfect term to describe almost all my piecing efforts. LOL Sounds much more technical and professional than “Shoot! How’d that happen?” Love your pillows and your blog. You brighten my day. 🙂 ~Stacey

    Liked by 2 people

  4. Wonder if I would ever start a project without the optimism bias???
    My learning about shrinkage came the reverse from yours. I’d calculated how many 1-inch squares I needed, laid them out, couldn’t believe how long the string was. Made it impossible to plan some color coordination.

    Liked by 2 people

    1. Good point – maybe it is the Optimism Bias that keeps us coming back for more/new crafting projects! “1-inch squares” – yikes! Isn’t that like a curse word? Ha!


  5. I love the comments here. 🙂

    ‘Wikipedia defines a planning fallacy as “a phenomenon in which predictions about how much time will be needed to complete a future task display an optimism bias and underestimate the time needed.”’ WOW this is ME!!! 😀

    Liked by 1 person

  6. Lol! I feel for Tierney! I have done that myself What was once gong to be a bead spread became a throw. It doesn’t Sean like a quarter of an inch should matter that much, or even an eighth of an inch, but add four of those squares together and you lose a whole inch! I still really love your smaller version. What great use of scraps:). — We started Lost in Space. Since you haven’t seen it yet, I will not give details, but there have been a few fun twists that make it quite fun. Have your started Fearless?

    Liked by 1 person

  7. LOL! Love the photo of the perceived plan and reality. How often does that happen to me…too many times to admit. I really enjoy lilac bushes as well. We have two in our backyard. They are so close to blooming. I’m waiting patiently for them to pop. 🙂

    Liked by 1 person

  8. Ha! This is every project I’ve ever worked on. At least I know what the technical term is for it now! 😂 And your pillow top still looks great, even if it did turn out smaller than you’d intended. It’s amazing how those little gaps between pieces and seam allowances add up, isn’t it?

    Liked by 1 person

    1. I figured I was not alone in my experiences – ha! Thanks for your comment. Yes you would think after 17 years of quilting I would have remembered the simple concept of “seam allowances” – not sure what happened 🙂


Comments are closed.