To follow a thread of this ongoing discussion about advisor-student matches.. there are certainly mismatches that occur, and it can be awkward to undo them.
Important information for the rest of this discussion to make sense: in my field, students work with a particular advisor from Day 1.
Over the years, I have had a few students switch to another advisor, and I've taken on a few who were switching from other advisors. In most cases, it was students who weren't doing well with classes, exams, or research and who thought that working with someone else might give them a fresh start. There are certainly situations of students switching fields/advisors once they get a bit of experience with the science and realize what their true interests are. I also know of a few cases of students switching because one advisor was too busy to give them much time, and another advisor provided a better research environment, and these switches have mostly been successful.
However, from what I've seen in my department, these successes have been much less common than the other kind of advisor-switches (i.e., struggling students trying to stay afloat). I guess we all want to give students a chance, or two or three, so we give these switches a try. From what I've seen, these seldom work out, but it would be nice to hear about some examples to the contrary.
2 years ago