Over eight years of building props and costumes I've noticed an interesting piece of human behavior. I have called this behavior by different names, but it started out as the "Lego theory." I realized the "Lego theory" while reading a blog of a fellow R2 builder who used a handful of lego blocks inside their R3 droid to give the clear dome detail. The real movie domes were very complex, filled with many unknown parts, electronics, and pieces. However, it is very unlikely that the prop departments from the movies would use Legos in their props and because Lego pieces are so iconic, they are instantly noticeable.
I came up with the "Lego theory" because I hypothesized that this builder used the lego blocks - despite these drawbacks - because they were easily at hand. Had there not been a pile of Legos laying around, they almost certainly would not have sought them out. Years have gone by and I've seen this behavior on my own projects and group projects as well. People's natural tendency is to use an item because it's convenient, not because it's right. They even try to post-rationalize why it will work, why it looks good, or why its the right thing. Yet, if given a menu of choices they would almost certainly have gone in a different direction.
Some examples of this might be reaching for the first can of blue paint you can find (or that you bought) and painting your entire R2. Or cutting a frame out of MDF because you don't have plywood on hand that day. Or trying to use a light in your dome that you found in your basement even if it doesn't really look like the real prop. Perhaps its adding that decade-old CD player to your droid even though the wiring is a mess, it barely functions, and a modern alternative can be had for quite cheap.
After years of witnessing the behavior and calling it out among friends, I've finally come up with a real name for the "Lego theory": I'm calling it the Primo Findo Fallacy. This theory states that people's natural tendency is to (perhaps wrongly) try to use and post rationalize the use of items or techniques because it is easily at hand or the first thing they found. It's far from scientific, but definitely something to watch out for as you build and create.