I was fortunate enough to have very good CFIs for my private/instrument/multi. Part of this was knowing what to look for (I come from a family of pilots), part of it is just the good fortune of them being relatively local (I went to a further airport than the closest one to me just for this reason, it added 30 minutes to the commute and was worth every extra hour of my life spent on the road).
Students should take on the mindset of quality of instruction has a direct correlation to your chances of survival, it may not be 1:1 but it is certainly a factor.
The CFIs who are good are ones who actually enjoy the job (hard to find them though in today's race to 1,500 environment, but they do exist, even some young ones!).
My take away is that no yelling is required and it is counterproductive.
A good CFI has a very strong set of communications skills and is flexible and adaptable to the way a particular student learns. Then if you aren't listening, they put you in a (relatively safe) situation where you see the err of your way(s).
A controlled yet bad situation that they allow to develop to a certain point because you weren't listening is for many a person a sobering reality check that I really need to pay attention or ask more questions if something isn't computing. It is ALL mental. My instructors never touched the controls except for initial landing learning/guidance, unless they wanted to demonstrate something (and asked for the controls, didn't just take them). I never had the controls taken from me, although certainly they would if a situation developed into an actual dangerous situation (which happened with some other multi students RE: low altitude engine-out mistakes), but I think this would be one of my initial evaluations of an instructor.
Do they (calmly) "use their words" and are tolerant of initially sloppy airmanship without needing to have feet planted on the rudders and/or hands on the stick/yoke all the time? Do they know how to let you get yourself into enough trouble and then talk you back out of it? Are they just interested in showing you how good they fly the plane and how poorly you fly it / an ego thing? Good instructors are like jedi mind trick guys, and what is rewarding to them is to take some poor sap like me and turn him into a safe and competent pilot with just their words.
Watch out for the ones who are not into it and just marking time to 1,500 hours, they are bad news for you and as I said there is a correlation between quality of instruction/mentorship and survival. You are buying the most valuable insurance policy by getting top tier instruction, and the muscle memory, habits, and way of thinking developed early on is a foundation that if it isn't right can be very painful to fix later.
As an aside I think the reason a lot of people quit (beyond economics) is that they don't have a mission, and it is a lot of work to go through if you don't have a mission, then it is just a matter of how strong is the passion, as that is the only thing left. Look at people who live in Manhattan, I know people who live there that don't have a driver's license, they don't know how to drive! It sounds crazy to many of us, but for them they grew up without a mission requirement, and so to them it makes sense.