What is English equivalent to 座右の銘 – a motto you always keep by the side?

Solution 1:

There is a concept of daily affirmations. An internet search will turn up hundreds of sites offering these sayings.

While many people in the US seem to subscribe to a regular consultation with these aphorisms, the term is often used sarcastically as exemplified by the Saturday Night Live character, Stuart Smalley (played by Al Franken, who has gone on to become the US Senator from Minnesota).

As an example of the positive effects of his philosophical contemplations, he ended every skit by looking into a mirror and telling himself You're good enough, you're smart enough, and, doggone it, people like you!

Solution 2:

I would say favorite motto or personal motto.