I learned the hard way to not underestimate how competitive and treacherous some people can be in the workplace. I was a long-term contractor in a large company and had an incident where I confided to another employee about some issues I was having negotiating my pay at contract renewal time. I never mentioned any numbers, just that a manager had previously promised me a pay-raise and was not honouring their word. Wi…
You can flip that and say the advice your co-worker needed to hear: don't be duplicitous or treacherous in the workplace. You may think it gets you ahead but this is highly illusory and temporary. When you look back you'll just have anxiety and regrets behind you, if you have decency. And when it's all over, the things you thought were really important at the time won't be, so why be a jerk about them?
That is, of course, if it doesn't backfire. Then you get nothing.