This doesn't always mean that insiders are dumping stock because they know the company is doomed. Sometimes yes, but when you have a company like Twitter where

This doesn't always mean that insiders are dumping stock because they know the company is doomed. Sometimes yes, but when you have a company like Twitter where a pretty significant percentage of compensation is in stock options and RSUs, then you're going to have lots of insiders selling in batches, so they can actually use that compensation to get things like houses and cars and diversified investment portfolios.