Perhaps an obstacle, according to the definition, can be to materialize something or create something as a challange to oneself? Sure, a log is a physical obstacle, but it is only a obstacle if you make it a goal to jump over it ”i want to jump over the log, it is not necessary, can i do it?”. In the same way one could ask ”i want to create a castle in Minecraft, it is not necessary, can I do it”? Jumping and building are both performances. This is just a guess though.