https://phys.org/news/2018-11-corporate-insiders-stock-loss.html

Generally speaking, insider purchases have very strong return predictability, but insider sales do not. Kelly, an assistant professor of finance at Notre Dame's Mendoza College of Business, wondered whether those insider sales might contain more insight into future returns than they appear.

While most traders purchase stock because they have good reason to think the stock will go up in the near future, there are any number of explanations for selling stock, he explained.