The Two Generals’ Problem

  • Published on:  8/12/2019
  • Time to tell a story about idempotency, computer science, and the Night of the Multiple Orders. • Sponsored by Dashlane —try 30 days for free at: BASICS: by Sean M Elliott and Tom ScottDirected by TomekGraphics by Mooviemakers mix by Haerther Productions to Dashlane for sponsoring the video! If you're techie enough to watch this video, you should be using a password manager. Get a 30-day free trial at'm at https://tomscott.comon Twitter at Facebook at on Instagram as tomscottgo


  • Tom Scott
    Tom Scott  28 days ago+2641

    Yes, I had help with the graphics for this series. There's no way I'd have animated that myself! On that note, thanks to Dashlane for sponsoring and helping me hire an animator: their free trial link is

  • Kinetik07
    Kinetik07 7 days ago+3709

    So it's like double posting by accident?

  • Putin did nothing wrong.
    Putin did nothing wrong. 7 days ago+355

    See you all in 2023 when this video gets recommended again

  • MarbleSwan666
    MarbleSwan666 7 days ago+109

    I find the idea of two armies going one by one through a valley sending acknowledgments back and forth until everyone is dead hilarious
    Just imagine the army in the castle being confused.

  • Brian Certain
    Brian Certain 7 days ago+219

    1:24 Spelled out "Tom" with the semaphore flags! ( ͡° ͜ʖ ͡°)

  • Philip Melchert
    Philip Melchert 7 days ago+241

    Everyone else: Goes to bed a reasonable time
    Me: Stays up all night trying to solve the unsolvable general problem with 0 knowledge of computer science

  • Kinetik07
    Kinetik07 7 days ago+3695

    So it's like double posting by accident?

  • Dominykas Turčinavičius

    "A single human error is never the root cause"
    A single human error: I'm about to end this man's whole career

  • z beeblebrox
    z beeblebrox 7 days ago+212

    idempotency: when you're able to have children, but just the one time.

  • Lysergesaure1
    Lysergesaure1 2 days ago+1

    7:40 you can definitely bribe the company to make the app send the master pasword to their servers, and none would be the wiser. Use something open source, and audited.

  • Ikis DragonFist
    Ikis DragonFist 7 days ago+93

    -"So what are we having? Chinese? Mexican?"

  • Sean O'Brien
    Sean O'Brien 7 days ago+3747

    Nobody would put a castle in a valley between two perfectly good hills, therefore the entire video is invalid.

  • Voodoomancer
    Voodoomancer 7 days ago+133

    Moral of the story: If you want to be a programmer, learn to cook.

  • Bibi Mizrah
    Bibi Mizrah yesterday

    Dash Lane is good. If you want self hosted multi device password manager that’s open source I recommend Bitwarden

  • Andrew Blucher
    Andrew Blucher 7 hours ago

    "A single human error is never the root cause"
    This applies to almost everything.

  • Maldus Alver
    Maldus Alver 7 days ago+50

    "Would you like to pay again?"
    Sounds like everything is working as intended to me.

  • Tamashii M. H.
    Tamashii M. H. 7 days ago+4858

    "If you're in computer science and work on a problem which involves potential loss of life, I really hope you're not watching a series called The Basics."
    And here I am. Because Tom Scott.

  • Netbattler11
    Netbattler11 11 hours ago

    you know this really seems like something which should have been at least mentioned in passing in my CS curriculum

  • Christian Rasmussen

    Neat. I'll float this to pupils who might appreciate this kind of problem. :)

  • Digeridude
    Digeridude 7 days ago+22

    A hill would make more sense than a valley. It would explain why they can't see each other.