Proper translation of "Faith in one's self" in Latin?

I took Latin in High School and I was thinking about getting a tattoo of the phrase, "Faith in one's self". Now, from what I remember the "one's self" probably would be some form of "ego" to show it in the singular possessive form of "I"? Since the use of the phrase is for a permanent placement, I'd really want to make sure that the grammatical use of it is correct. Thanks!