While all Chivalric virtues are best expressed in balance with one or more others, the two that are most closely bound are Faith and Reason. First let us create working definitions for these: Faith is the belief in an idea without the need for evidence, while Reason is the examination of an idea through logic and facts. It is easy to see how these two concepts so easily come into conflict with each other.
Let us take as an example having an officer position to fill in your local SCA group. There is an energetic young candidate that you feel could be a good fit, but they have no experience. Listening to Reason alone may cause you to pass up someone with great potential, while Faith may lead you to overlook important flaws. Here the tension between the the Virtues is about the ability to take risks. Without Faith, one cannot take risk, while without Reason those risks will too often result in disaster.
I have faith in my knowledge of costuming and dance. I can make garments I have studied quickly and consistently, and I can teach the dances in my repertoire at the drop of a hat. However, I often go back and look at the sources again, and sometimes I find that my memory has shifted from what is really there, or there is new evidence that has been published or that I failed to see before. Faith allows me to be productive without second guessing myself at every turn, while Reason keeps me from unwittingly propagating bad information.
As a final exercise, let us consider our relationships with others. We make decisions about people, both friends and enemies, and it is easy to leave them in those categories once they are placed there. We have Faith in our ability to judge the character of others. However, a friend may change, or show previously hidden flaws, and that friendship may need to be re-evaluated. Likewise someone we decided not to place among our friends may also warrant another look, either because they have changed or because there we failed to see what was already there. Reason tells us to look for new information and update our assumptions regularly, though Faith keeps us from being exhausted by constant revision of our social groups.
Balance, as usual, is the place where we should strive to remain, even though it requires the most effort and mindfulness. Check in with yourself from time to time. Look at things with new eyes or let go of the reins for a bit and trust that you are going the right way.