I was working at a Big Startup, on ML side of things. All the senior engineers in my team left and me and a few others became the senior-most engineers (with <1 YOE). The models we built were contributing 100M$+ to the top line of the business.
My then manager tasked to do some data analysis to determine whether building a "new nonsensical ML Model" was the right way forward. I like a diligent bee crunched the data and came to the conclusion that "we shouldn't build the new model".
I showed the results to my manager who laughed and told me to do it again. It's also important to note here that my team lead and old manager had left the company. This person was completely new and a senior manager.
I in my naive mind (and oblivious to politics) thought he's telling me to say that the results "do make sense". and that's what I said. We even presented the results to product people who gave us go ahead. Since we were doing such pivotal work, even the company's CTO was involved and tracking our progress.
The next few months were one of the most painful times of my life. Immediately after the meeting, we were tasked to actually build those models. I knew that they wouldn't bring any results, everyone else in my team knew, even PMs knew. Everyone except the manager.
I led a few interns and we built the damn models and got the expected result which is 0% improvement.
What happened next taught me a lot about life. Their was a meeting (which I wasn't a part of) where everyone senior who had their ass on this project came together. They invented a "new metric of success" and asked us to train ML models optimizing for that. We trained the models and obviously since the optimization target changed, we saw improvement.
Then we created charts according to that metric which were obviously good. the PMs showed slides to Upper management. and all was well again.
The best part of the new metric was that the actual results will only be visible years down the line. So we called it a success regardless. I switched my job soon after that.
I learnt from this experience to just say "NO" firmly on doing things I'm not comfortable with. and always keeping a text trail. The manager was kind of an oddball so I never fully got whether he actually knew this from the start or was just plain incompetant.