Imagine going into an environment suffering some serious performance issues adversely affecting the day-to-day operations of the business. From initial conversations it seems great. You're asked about how you'd handle, "difficult personalities" a fair bit, but aside from that, seems like you can add a ton of value. In your first days, you exhaustively quantitatively measure the entire operating environment, prioritiz…
Yes, this is the problem. Unprofessional, low-quality employees think employment is "king of the hill," when really it's "tides lift all boats." It only takes 1 person in a company of a hundred to completely destroy it. Allow one psychopath into your company and it'll go bankrupt or otherwise defunct within just a couple years. These folks are afraid. They know their performance is substandard. They exist by hiding t…
Very few people believe teamwork is a rising tide because very few companies do.
A perf improvement that takes something from hundreds of minutes down to 1.2s does make the person who did the original implementation look bad. Questions will be asked why it was so much worse before, especially if those minutes came with an associated cost like build minutes or something, and doubly so if the original author has been claiming any improvement is impossible.
Those people may be concerned that they've been knocked down the hill, but they're also probably concerned they'll be seen as incompetent and a liability, and could be fired (rightly so in this case).
A company will often see an improvement a new hire makes less as making something better, and more as fixing the existing employees' mistakes, with absolutely no consideration given for why those mistakes were made.