How do you separate you from your understanding, FK?
I separate me from my understanding by keeping faithful to what scripture says. My sinful nature would love to interpret scripture to allow for all sorts of sins. We have both seen nutjobs of all stripes use scripture to try to legitimate everything from adultery to abortion to homosexual conduct, etc. Those might be the easy ones, but I have definitely caught myself before trying to justify something I wound up deciding was wrong because of a more honest look at scripture. I take those occasions as concrete evidence of Holy Spirit's personal leading. And so, if in accordance with scripture Holy Spirit leads on these occasions then it follows that He leads individually as a general matter since no distinction is made in scripture. The Bible just says that Holy Spirit will lead us "in all things".
Now, concerning why all Christians don't have the same interpretations it should be noted that all Christians are at different places in their respective walks with the Lord. There are some spiritual truths that some are just not ready to handle yet, so Holy Spirit deals with us accordingly. It doesn't mean He leads in error, just that He may lead in varying "doses" or in varying levels of understanding. I'm sure we would agree that any given verse or passage could potentially have more than one fully true meaning. So for example, at one point I felt led to hold the Arminian view of cooperation. It can certainly be argued that the Bible has support for this. But now I believe the Holy Spirit has taken me to the next level in Reformed theology, also arguably supported by scripture. I don't think I could have made the jump directly so I believe it was necessary to get me there in steps, which is what I think Holy Spirit did. Undoubtedly I have many more steps to go concerning many many issues and I can't wait to have them revealed to me. All of this makes sense because Christian growth, whether through the leading of the Magisterium or Holy Spirit directly, is a life long process.