Wow. Talk about being extreme. Look, I'm about as realistic as they come and I respect NOsaintsfan, but, I honestly disagree with his/her outlook on your future considering we know nothing else about who you are, what you have accomplished, etc...
First off, we don't even know what class the guy failed (not that it REALLY matters to my point, but failing nutrition or something like that vs medical physiology is a big difference). Second, have you ever seen what program director's get when a med student applies? Just bc the guy failed one course doesn't mean every residency he applies to will receive a red piece of paper with the words, "failed course," printed on it. That's just crazy talk to inform a M1 student that they have "realistically" ruined all of their chances of getting into competitive residencies because of this guy's situation.
Anyway, to the OP, it takes some people longer than others to develop that critical thinking skill that is required to do well and pass exams during medical school. Hopefully, this failure is just one hiccup during your time in medical school. Basically, continue to work hard and do well on the rest of your courses in years 1 and 2, crush your board exams (both COMLEX and USMLE if you are planning on applying to MD only) and make a name for yourself during your clinical rotations so that the LOR's you get are strong. If you do these things, you should get a dean's letter than is full of so many positive things that this one failure might not even get noticed. Also, your residency application is usually screened by the program's secretaries who are basically looking at your board scores and your class rank/GPA. Thus, you can imagine if you do a rotation at a residency you are interested in, meeting and getting to know the person who screens the apps can never hurt. Once you get an interview, if one ever questions the failed course (which may never happen if you crush your boards), then you will be able to explain, with confidence, why it happened and all of the positive things you have accomplished since.
Bottom line: Your door is not shut on anything. Step 1 represents years 1 and 2 of medical school, thus if you crush it, then there should be no question that you have mastered the required material. If there is something you want, work hard and go get it, and if, unfortunately, you don't match want you wanted, at least you will know that it wasn't
because you didn't work your ass off trying.
Good luck!