Being a draftsman is a bit like doing a maths exam every day, one where you should not make mistakes at all. But ask yourself: who ever scores 100% day in day out? All we can hope for is that our mistakes are minor and easily fixed.
I remember the story of one draftsman who drew an entire truckload of ducting. On the day it was delivered, he was looking out the window. As soon as he saw it he realised they were all completely wrong.
Another, an architectural designer, was awoken at 2 am in the morning. Apparently the irate person on the phone accused him of bad design of a deck because there had been a party and a large number of people were on the deck and it collapsed resulting in some injuries. A real shock to him, but he was later vindicated as it was found the builder had just nailed the stringer support to the house instead of using coach bolts!
Anyway, I seem to be sliding back into drawing houses for fun-it is great, just as long as you do not intend to build them!
The "flying saucer" one came from a vision I had of standing inside a house and looking upwards and seeing the sky: ie a hole in the roof! Hardly original. Maybe the glob below the hole made of chrome is though (probably not!). The "pears laid on the ground" one is again probably not original, but has the "looking at the sky while inside" thing going as well.