If you repeat foible out loud enough times, it sounds so funny that you can laugh at it and maybe remember to laugh at the odd and distinctive weaknesses of others — the foible or two or a hundred that we all have.
Sometimes a foible helps make a person who they are, even if the foible, or weakness ("feeble" is a close relative), is a little odd. Synonyms for foible in a negative sense are "failing," "shortcoming," and in a more positive sense "quirk," "eccentricity." It can likewise be annoying or endearing. Most people have a foible, or idiosyncrasy, that stands out to others, but interestingly, a person rarely sees his or her own characteristic foible.