As we go up the ladder of success, changes are inevitable.
You of course get a higher (if not better) pay, your responsibilities increase, and for most, you get new people who work under your supervision.
While a promotion or a step up the ladder is good news for most, there are also changes in the dynamics of people who used to be just within your same level.
If some people play their cards right, they would slowly gain the respect that is incumbent in the position, if they are wise enough their staff will almost always defer to their decision-making skills, and if they are smart enough they will almost always be on top of their game. A person emulated, admired, and respected.
But sometimes, people lose track and balance. In the attempt at getting better at work or coming up with decisions (hard, trivial or otherwise) some relationships are eventually strained. On the other hand, a boss who focuses more on maintaining the good relationship from former colleagues end up trying too hard in remaining friends, with decisions affecting friends clouding their judgment. Either way, it is the staff that is usually at the losing end of the bargain. A helpless pawn.
But eventually, everyone loses.