In general, medical schools are willing to work with students to ensure they meet the degree requirements. Attrition rates are very low for US MD medical schools (somewhere around 3%, I think).
A couple of years back the AMSA student magazine published that the attrition rate nationally at US allo schools was about 5%, with 1.5% due to academic reasons (ie failed out), which I believe are still pretty close to the current numbers. As mentioned above by Perrotfish, some med schools never fail people out, so that (1.5%) means that other med schools out there are failing 2-3 people each year. From a class of 150-200, a failout rate of 1.5% isn't a ton of people. If you are willing to put in the work, and change up things when you find them not working, it probably won't be you.
As far as matching is concerned, about 93% of US allo seniors who enter the match match each year, with most of the remainder snaring spots in the scramble. So odds are very good that if you get into a US allo med school you will graduate, and if you graduate, you will land a residency spot.
I do suggest that saying it's hard to fail out and that it's easy to pass are really two very different things. Maybe it's easy to pass at some of the programs out there, but certainly not all. (In truth, I think you get a lot of bad advice on SDN on this topic because whenever folks ask about failing out, someone from one of these programs which has never ever failed someone out chimes in -- that is not really the majority BTW). I've seen a few people fail tests, courses, and even whole years. Med school allows folks to remediate and gives lots of second chances so these folks all do graduate eventually (but maybe not in 4 years). Odds are very good at most med schools that you are going to see one or two of your first year classmates still be a first year as you progress into second year. It happens. They still have a career.
The folks I've seen repeat first year of med school were science majors with strong undergrad backgrounds, and who you wouldn't characterize as lazy in terms of hours. But the big trick with med school is that part of what you learn in the first block of med school is how you learn. And it ends up being a very individualized process, and to some extent is more important than the material itself because it's what's going to serve you for the rest of this career. What worked in college very often doesn't work in med school, I'm afraid. There are lots of tried and true methods you are going to find really don't work well for you. Some people learn well in groups, some do best solo. Some need to attend every lecture, others get more from reading primary resources. There will be folks who live and die by flashcards, and others who draw detailed flow charts. You may find you are spending a ton of hours but not efficiently, such that you are really spinning your wheels. And if that's you, you won't do as well on the test as the person who has mastered getting info into his brain more efficiently who puts in half the time. That doesn't make the person lazy, but might make the person at risk for not passing. And that's the key - med school poses two challenges (1) covering a ton of material, and (2) learning how to get that info into your brain effectively and efficiently. I guarantee you a few folks are going to come out of undergrad thinking they know how to study and yet seriously struggle in the first set of exams. And they will be extremely frustrated because they know they put in more hours than some dude who smoked them on the test. It happens every year. Doesn't mean they didn't put in "the bare minimum of effort", or that they are lazy or that they are stupid. Just means they didn't get efficient yet. And if they go to a med school that does fail people (most of them), they can be at real risk to fail a test, a course or even a semester. But again, if that happens, they get a second, and probably a third chance. (Which is the real reason it's hard to fail out altogether.)
