None of the non-radioactive elements ever spontaneously changes into an element with less energy. There are barriers. One of these natural atoms must gain energy, before it can finally go downhill to a lower energy. It is said that each of these atoms is stable.
So, I was concerned with supplying the energy to transform lead to gold. But a second problem occurred to me. What if my lead atoms went downhill and turned into something besides gold? It is not so bad to accidentally turn lead into silver. But turning lead into zinc could be quite embarrassing. So I began to form my theory that a lead atom needs an adjacent gold atom to "emulate." To carry the anthropomorphizing further, it seems natural for the lead atom to "want" to become a shiny gold atom. Luckily, this idea not only seems to change lead into gold, but at a much lower temperature than might be expected. The mysterious philospher's stone of the alchemists turns out to be gold itself.