Why do projects always take longer than expected?

I want to make a bet with you. Think of an important project you are working on that you expect to complete sometime in the next few weeks or months.

*Now try to make your most accurate estimate of exactly when you think that project will be completed.

*Now estimate when it will be complete in the best case scenario, if everything went as well as possible.

*Do the same for the worst case scenario, if everything went as poorly as possible.


All done? Here the deal, I bet that you won’t finish that project until after your worst case scenario estimate.

Why so pessimistic? It’s called the planning fallacy and it affects everyone, especially me. People tend to make overly optimistic predictions of how long things take to do. And despite the number of times this happens throughout our lives we still fail to adjust future predictions to account for it.

Had I given that set of questions to myself at the beginning of this year and tried to plan when the TestrBot project & subsequent experiments would be done I would have been off by months.

I think the cause is that our predictions only account for the sum time of each step of the project and we forget to include time for distractions, unanticipated contingencies, and annoying things like human needs getting in the way.

Additionally, I get distracted easily. I work a lot but my efforts get divided in too many ways. Every time I turn around my car needs gas, my wife & dog need a belly scratching, and when I finally sit down to pump out some awesome articles my darn body starts aching to outside and exercise.

beatiful day outside

Shit, it’s a beautiful day outside. Guess I’ll be finishing that project tomorrow then.

The lesson here is to remember that things almost never go exactly according to plan. Everything takes longer than you think it should, so plan accordingly by adding a fat safety factor to your project timelines. A great way to bypass your overly optimistic brain is to pretend that you are having someone else work on the project for you rather than doing it yourself. This helps us be more realistic because we can’t help but see others as being slightly less awesome than ourselves.


None of this is to say that I don’t have some TestrBot test results to share, because I do! Just give me an hour to write up a blog post for it real quick…. actually, better make that 10 days to be safe.



  1. Reblogged this on The Arts Mechanical and commented:
    It’s the unplanned gotchas that get you. In my last project I needed to make 10 brass catenary poles for my HO Scale Shinkansen photo module. Because nobody made those poles I needed to turn them on my lathe. for that I needed to make a special tool. I spent two months making my first iteration of the tool only to find out it couldn’t work. Blog post to come when I make a new tool that does the job.

    Liked by 1 person

  2. Since you are a young fellow, you probably don’t have to calculate in age effects into your project time. A majority of my projects involve one of my two cars (certified car nut). I typically estimate how much time it will take to complete my projects and am pretty good at estimating purchases. Its the fabrication times that I falter on. I’ve noticed a general rule. If I believe a project will take me, in my mind’e eye 3 hours to complete, it will actually take me 7 hours, with the age factor added. I’m 62 next week with alot of injured extremities (Knee, Shoulder, elbow). I replaced front brakes with a Wilwood big brake system on my 2014 Fiesta ST. I estimated it would take one hour per side to disassemble the OEM brakes, 2 hours per side to assemble the rotors, install and center the calipers, and 3 hours to bleed the brakes,so a total of 9 hours. I forgot to add 45 minutes purchase a star socket to attach the hub to the caliper. It ended up taking me twice as long due to the age factor, but in the end, the new brakes work fine, even if it really took 18 hours. I laugh when other bloggers state that it took them 5 hours to complete some car modification, as I know this number is their optimistic version, not the actual version, no matter what their age. My motto is, if it can go wrong, it will go wrong, and take way more time than you think.

    My next project involves wiring in a flex fuel meter to verify that I’m running e40 fuel mixture. That should take 4 hours times 2.

    Liked by 1 person

    • Good story, thanks for sharing! I didn’t even think about that, but I’m can see the potential for age related problems to slow thing down even more. On the bright side I’m sure you waste much less time that I do on experience related mistakes.
      I hope I’m still physically able to make things the way I do now when I get older.


  3. When I started working in an Agile software team, I realized that one big reason my past estimates had been so far off is that I didn’t know or remember how long things actually took. I love Agile for emphasizing a) how big you think a task is (your estimate) and b) how long it actually took (in hours spent, not days elapsed).


Leave a Reply to EngineerDog.com Cancel reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.