Both after reaching the peak of the Concealed Stage and throughout the Sky Human Stage(possibly even higher) or for a being undergoing a massive change, the Heavens or some other existence responds with summoning thunder from the sky to strike whoever or whatever is undergoing this change, causing them to enter a Tribulation by thunder. Easily referable to Lightning Tribulation. There are 3 situations that can happen now, The person experienced a problem or was not prepared or some other scenario and is incinerated dying immediately being turned into ash. They could also still fail but have better luck or just fare better and just end up wounded and not dead, this could either ruin them completely or they can try many times over with ever-increasing odds. And the last result is that they succeed which will make a said person enter a weakened state but will temper them and make them much stronger.
After reaching the peak of the Concealed realm and passing into the Sky Human realm(Same applies for Yao Beast transcending into a higher realm along with other existences) all must without known exception go through a Lightning Tribulation. Although it is the easiest tribulation to go over it is still a boundary that many will never be able to overcome, at least in worlds Similar to the Eternal World that Chen Feng lives on.
Throughout the Sky Human Realm in order to advance, starting from stage one going up to stage 9, receive and ever increasing level of Lightning Tribulation. Any Lightning Tribulation in any higher realm is still unknown.
When transcending into the Human Immortal stage a drastic change will happen to the tribulation and will change depending on the person, depending on one's innate talents will equal to what tribulation they get. by this I mean if you are talented in both fire, metal, and wood, those will be the corresponding tribulations you will get. so the more talents you have with the elements will equal to how many more tribulations you will have. So you could only be good at one thing and only get a single tribulation or two. Or you could be a genius of elements and have much more.