That is not necessarily true. As an employee, you may be in a good position to judge whether a firm is likely to succeed, with perspectives not available to the market. This is why markets often react when CEOs buy/sell their own stock.
The average employee would be in a terrible position.
Ref: Enron.
Isn't it more likely that you don't know your employer as well as market analysts, but that you do have much more severe cognitive biases?
A CEO is an "insider" in market-speak. Jo(e) Engineer is just a punter like anyone else.
That's not strictly true. Depending on the company, it's very possible for mere engineers to have access to material non-public information. There's a reason many companies impose broad blackout dates on trading.
Mere engineers would be prosecuted long before CEOs for the totally-at-Justice-Dept-discretion crime of "insider trading".
That's self-evidently false. Engineers have insight into the internal culture of a firm and how it may differ from public perceptions, not to mention their own opinions on the quality of the back end technology and awareness of future plans or possibilities.
The advantage of the employee isn't insider knowledge - it would be illegal to deal based on it - but understanding what the company does and which market it works in in the first place. This purely technical knowledge might give investment decisions some better factual support. But