What does this sentence mean: "It is easier to make a 3-inch mirror and then to make a 6-inch mirror than to make a 6-inch mirror from scratch"?

It seems to say that A is easier than B, with A being "make a 3-inch mirror and then to make a 6-inch mirror", and B being "make a 6-inch mirror from scratch". But why that makes sense?

  • 2
    You've gained experience with a simpler but very similar task. – Edwin Ashworth Jul 8 '17 at 23:30
  • Would you elaborate? I am still confused. – zell Jul 9 '17 at 0:03
  • Your question reads "it is" and should read "is it." – MAA Jul 9 '17 at 0:37
  • Oh, I see the question mark is not part of the quotation :) nevermind – MAA Jul 9 '17 at 0:38
  • It's what @EdwinAshworth said but I wanted to make sure you were clear why and also explain the meaning a littler further. It's saying that it's easier to get to the 6in if you already have a 3in because you only need to add 3in. It does not mean that it's "logically" simpler. Nothing at all to do with the logic of the scenario. It just means to say you should take small steps and learn by doing smaller things first. You have heard the phrase, "You have to learn to walk before you can run."? Same thing. It means to attempt small tasks before you tackle larger ones. – Kace36 Jul 9 '17 at 7:20

I don't know why they use mirrors for this example, but the concept of making a small model of something before making the full sized thing is common.

For example, this company is building a smaller demonstrator aircraft capable of supersonic flight, before they begin building the full size passenger airliner. The reason is that it will be less expensive to learn from their mistakes on the smaller version. This way, when they go to make the larger full size aircraft they have figured out all the technical issues of making it. I guess this is like making a little mirror before making a larger one.

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