Of course Nutella, thanks for the information! So the random thing is not that random after all, and with hight free will you never know what they might do if they're not busy!
So my sims never had a skill elixir, what I did was that they were both bookworms, I sent them to the library and placed there the incense and a boom box! I let them read only the first two book, otherwise they wouldn't get any challenge. I first sent them to the future: Tobias learnt bot building by reading books and Tris took a class of advanced tech and then stole a windcarver and a couple of sprites and then it was only Tris who did all the traveling and the photography going around in the windcarver instead of walking, but I think she learned more of the advance tech from the Sprites. The bot building skill Tobias learned only from reading books because I was afraid to add a Simbot to my household unwillingly, then I learned that it wouldn't happen. It was funny that they could only stay in the future for two days, because of the challenge rules, and Tobias wasn't done with his "Bot building 3" yet, so I sent Tris to buy one for him and when they were back home I found out he had taken the book from the library with him, how does that happen? Why and how do Sims sometimes steal books?