> Good work very much doesn't speak for itself

Some people are obviously very intelligent and for people with enough technical abilities this can be spotted (e.g. because they churn out a large volume of high-quality code with almost zero defects). I have definitely seen this.

But I have also seen a colleague getting promoted that took thrice the scheduled time to deliver on a low-impact project, planning 2-3 long meetings a week, with about 8 people, discussing details for hours and hours (of course without writing anything down). When he went on leave for a few weeks, leaving a significant backlog of work and noting to our manager that "it's trivial to release", I actually managed to release it. At the end-of-year review he was praised for "deliviring such a complicated project", while the higher impact project I worked on and delivered in 1/3rd of the scheduled time was seen as a "simple project" because it got delivered without any hiccups.

Often it's also just a matter of "this guy states facts with confidence so it seems he knows what he's talking about" (even when he gets the facts wrong). At some point I just stopped correcting him because if we disagreed people would just assume I was wrong. In other words, being good at talking helps your career a lot.