I was once walking with a young tzurba d'rabanan and I commented that something he said was not in accordance with the Mishna Brura. He replied, "There are other poskim besides the Mishna Brura." I am sure this is painfully (literally, I fear) obvious to all; I am not at all good about keeping my mouth shut. That time, however, I showed uncharacteristic restraint and discipline. Actually, I was probably just in shock and realized that I wouldn't even know where to begin. Between you and me, however...
I know there are other poskim. As it turns out, of course, the Mishna Brura also knew that. He also knew all of those poskim, plus more, plus had a deep understanding of the gemaras. So I read a few poskim myself and draw my own conclusions, or I can take advantage of the Mishna Brura's uncanny grasp of kol ha'torah kula. Moreover, when learning more recent poskim, it is clear as day that they treat the Mishna Brura with special reverence. When I had cancer, I let my doctor in consultation with the hospital medical board plan my treatment. That's just for my life in this world; obviously for my eternal soul I am even more cautious!
What brought this up was learning a long Biur Halacha on a seemingly minor (though important) detail in making the strings for tzitzis. In order to become tzitzis strings, the sheared wool must be: carded (m'nafeitz), spun (tavui), and twisted (shazur). Everyone agrees that the spinning must me done with the specific intent to produce the strings used to make tzitzis as HaShem has commanded; aka "lishma". The quite long Biur Halacha (Siman 11, syef 2, d.h. lishmahn) addresses whether the twisting needs to be done lishma. He first demonstrates that the poskim who say that the tzitzis strings don't even (b'di'avad, mind you) need twisting are off the mainstream and one may not rely on them at all. He also demonstrates conclusively that they definitely should be twisted lishmah and that making them with specific intent that they not be used for tzitzis strings certainly renders them pasul, even b'di'avad. What's left? "Stam da'as"; that is, can we rely (at least b'di'avad) on the general principle that "kol ha'oseh al da'as ha'rishon oseh"/all that is done in a process is done according to the intent expressed at the beginning of the process? The reason there is a question is because this is two processes (albeit done by one person), spinning followed by twisting. Can we, for a d'oraisa requirement, extend that principle to include a second process (twisting) that is a follow up to another process (spinning) that was done with proper original intent.
The Biur Halacha answer, "Why... yes, you can."; based on a gemara in Z'vachim (animal sacrifices). Oh, surely he means a gemara about tzitzis that happens to be in masechta Z'vachim, right? No, sir; he means a gemara about shechting and receiving the blood of the korban pesach. Eh? The cases are actually precisely parallel: a process that has a pasuk requiring lishma (spinning vs. shechting) followed by a process that is not explicitly required to be lishma (twisting vs. receiving the blood); the gemara concludes that "kol ha'oseh al da'as ha'rishon oseh" does, in fact, apply even when it is two processes (but done by one person).
That Bi'ur Halacha is a whole shiur on how to read poskim, how to resolve contradictions in poskim, how much weight to give to a p'sak by different poskim, and even how to take apart a gemara.
So next time someone says, "There are other poskim besides the Mishna Brura," ask him if he's learned that Biur Halacha. When he says "no" (because if the answer were "yes" he never would have made that comment in the first place), just be quiet. Trust me, it's not worth your breath. Besides, I'll motzi you... I still can't keep my mouth shut.