"I had a difficult time defending my academic pursuits to my father. He was disappointed. He can't relate to my passion for comparative mythology. He doesn't feel like I will make any money at it and expects me to play it safe like he did, and his father before him. I knew the situation would turn into conflict, and it did, but I had to face it, and now it's done."

Keep your example academically related, as opposed to volunteering something along the lines of not following through on your commitments as a result of other pressures in your life. Doing so will only warn them that the same might apply here.

Oxford advertises that a common denominator for their students is "the ability to think deeply, the ability to look at anything, whether a newspaper article, a piece of research or an object, and instinctively start considering the theory behind it, the potential impacts on a wider level, your own position and thoughts about it, what other people might think. It's the ability to absolutely refuse to take things at face value." Consider this when coming up with an appropriate example for this question.