Everyone has reason, but there is a choice to use it or to stick with what has been "working." This is the battle between empirical observation and mathematics.

We tend to use faith when we're not comfortable with our skill at reasoning or with the mass of facts about whatever we're considering. The kind and explicit way to say this is "I think I understand your argument, but I can't trust what I know and my powers of reasoning enough to actually behave as though you are right, so I am choosing to continue in what you might call 'the error of my ways.'" However, this approach requires a person who understands him or herself, has more humility and maturity than most of the rest of us, and who just isn't interested enough to figure it all out. I'd say extremely mature, but a little lazy.

Some people, like me, readily abandon faith when reason seems to contradict it. In many cases, this abandonment has to be reversed later because the reasoning behind it either contains some logical fallacy or some incorrect "facts." Then there are those times (Gallileo - well, he's a person, really, but think of the time he fought for his view of the heavens, for example) when we're right and we can't find any reason to deny it, except perhaps to suffer less at the hands of prideful, mistaken moral bullies. Fortunately for me, I have never suffered so much that I was forced to pretend I believed something when I actually didn't.

We tend to use reason when we think we know enough and we're confident in our reasoning skill. Both of these things can be misjudged, and the worst examples of it can generally be found in politicians. Some think they know enough to solve big problems, and they are over-confident in their ability to reason their way along the best path. This leads, for example, people like Hitler to bring about great atrocities such as he encouraged.

So you see that in my opinion, sometimes it's better to use faith and sometimes it's better to use reason, and we can make mistakes either way. The safest path is big on humility, honesty, and paying attention.