Left Coast,
re: "... if we're convinced something is true, we believe it already."
Correct. Once we are convinced of the truth of a thing it is too late to consciously choose to believe it because we already do.
re: "We don't choose to be convinced, it just happens."
Correct. It's most likely due to some process which takes place in the subconscious as a result of an exposure to stimuli, such as literature, lectures, media, conversation, reflection, experience, etc.
However, a number of folks are saying or at least implying that they can consciously choose to believe things. Perhaps one of them can help me. I have never been able to consciously choose any of the beliefs that I have and I would like to be able to do that. If someone here thinks that they can consciously choose to believe things, I wonder if they might explain how they do it. What do they do at the last moment to instantly change their one state of belief to another? What is it that they do that would allow them to say, "OK, at this moment I don't believe that ‘x’ exists or is true, but I choose to believe that ‘x’ exists or is true and now instantly at this new moment I do believe that ‘x’ exists or is true?
Maybe they could use something like leprechauns to demonstrate their technique. According to the Encyclopedia Britannica, a leprechaun is "a fairy peculiar to Ireland, who appeared in the form of an old man of minute stature, wearing a cocked hat and a leather apron" and who stores away his gold in a pot at the end of a rainbow, and If ever captured has to grant three wishes to the person who captures him.
And if beliefs can be engendered by simply choosing to have them, then evidence is not necessary - prudent in some cases perhaps - but not necessary.