Near the end of building it, I needed a light grey 1x4 plate (the plates are the little thin pieces that are 1/3 the height of a standard brick)... but I seemed to have trouble finding it. This often happens when I open up all the bags of bricks and dump them into the box and start building; small pieces have a tendency to hide under large ones.
But I lifted all the large pieces, and even the model in progress itself, and I couldn't seem to find it anywhere! Well, I thought, maybe I dropped it on the floor somewhere and didn't notice. Or maybe I used it when I should've used a dark grey 1x4 plate, or something.
The thought that Lego might've screwed up and put in one too few light grey 1x4 plates occurred to me, of course, but I dismissed it, because I've read about the company: Lego's quality control department is one of the best in the world! They've NEVER let me down by leaving out a piece, EVER.
My quick-fix solution was to go into my pre-existing Lego collection, find a spare 1x4 plate, and use it. So I finished the Lunar Lander, and it looks nice! Just like the real one, with radar dishes and sticky-out stuff and a ladder on one of the legs, and two astronaut figures, and the top part even separates from the base!
And I found a stray light grey 2x4 plate left over. Well! I must've used the 1x4 where I should've used the 2x4. So I carefully looked through the instruction book... and guess what! There's one step where the little "parts needed for this step" diagram shows a 2x4, but the main diagram shows a 1x4 plate being put in! The model itself is a masterpiece of design, but the instruction booklet was apparently a rush job! Another telltale sign: some odd artifacts on the diagrams where the shading on the pieces had this weird digital jagged edge.
(And that solved another mystery I had, which was why two of the slope pieces on the back were attached in such an unstable easy-to-break-off way; they were *supposed* to sit firmly on the protruding 2x4 plate, not hover precariously over the space where the 1x4 *didn't* protrude!)
So I partially disassembled the thing, put the 2x4 in its proper place, and returned the spare 1x4 to my collection. Then I put one of the little Lego astronauts on the ladder. That's one small step for the little plastic man; one giant leap for me and my brick detective skills.