The reason: the CEO is acting in a weird unstable way.
Today, the shares soared because of a tweet Elon Musk issued that he might take Tesla private.
Only he won't be able to because who is going to lend him the $82 bn to buy all the shares to take the company private, when it is already loaded up with debt?
Tesla is not making any profits - instead it is burning through cash raised by investors and venture capitalists. Tesla keeps missing deadlines, and the CEO seems to be erratic and unfocused. Last month, he suddenly decided that he wanted to get involved in the rescue of a group of Thai children who had got trapped in a cave, despite his lack of experience in cave rescue. He flew over there to take selfies of himself (getting in the way of the actual rescuers). Amd when the real rescue team politely told him that his services were not required, he accued one of them of being a pedo.
For starters this is not the way a normal person behaves, let alone a CEO. Secondly, with Tesla missing deadlines shouldn't Musk focus on the job at hand instead of getting distracted by stunts?
If you own Tesla shares, take advantage of today's price rise and sell. The shares will come back down to earth when it dawns on people that Musk hasn't the ability to take his business private, and meanwhile the real shareholders and lenders are getting twitchy and will likely not provide more funds for him to burn.