I once had a doctor get on my case when I had an ear infection for not taking all of my antibiotics I was prescribed. (Ear infection still went away though)
You really should take the full treatment if you take antibiotics. Not for your sake, but so we don't have antibiotic resistant strains running around.
Yeah, the way it works is this: Imagine you've got a few million bacteria in your ear. Now, when you introduce antibiotics, those bacteria naturally have enough mutation that they respond differently to the antibiotics; they don't all die at once. It's your typical bell-curve distribution, where some die off immediately, the vast majority die off shortly after, and then some survive fro a good long while before dying off. If you don't finish your antibiotics, you kill off only the low end of the bell curve; those in the first and second categories. You've now killed off 99% of the bacteria, and so far as you can tell, you're well again. Most of them are dead, and you feel fine by day 2 of your 7 day prescription.
Except that now, you've got that resilient 1% of bacteria left. Each and every one of those bacteria will begin reproducing, now that you've killed off their competition for resources and stopped taking the antibiotics which were slowly killing them off. As they do, there's once again random mutation. A few days/weeks later, your infection comes back; or perhaps some have transferred elsewhere into the environment. Due to having killed off the lower 99% of the bell curve, this new normal distribution of mutations has its center at the extreme edge of the origin distribution; some will be killed off after a while of that antibiotic, but most can survive for long periods of time with that particular antibiotic. They may not be entirely immune, but they are highly resistant to the point where you simply won't be able to effectively kill them off with that particular medicine anymore. Congratulations, you now have antibiotic resistant bacteria in your system.
For something generally minimally-contagious like an ear infection, this may not be too bad (aside from having an ear infection for several weeks that is); you just take a different antibiotic the second time. However, the bacteria causing that ear infection isn't the only bacteria you have in you. Antibiotics effect all bacteria in your body at the same time, be they in your ear or in your gut. You may be aiming to cure the ear infection, but you're doing the same thing to whatever other bacteria you happen to have in you. Which is why you really need to finish any antibiotics you are prescribed; you may feel better, but if you don't kill off all the bacteria, you may simply end up breeding the next MRSA.