The first thing to do when you are upset is to notice that you are. You begin by mastering your emotions and determining not to go any further. With this superior sort of caution you can put a quick end to your anger.

[El primer paso del apasionarse es advertir que se apasiona, que es entrar con señorío del afecto, tanteando la necesidad hasta tal punto de enojo, y no más. Con esta superior refleja entre y salga en una ira.]

Baltasar Gracián y Morales (1601-1658) Spanish Jesuit priest, writer, philosopher

The Art of Worldly Wisdom [Oráculo Manual y Arte de Prudencia], § 155 (1647) [tr. Maurer (1992)]
    (Source)

(Source (Spanish)). Alternate translation:

The first step towards getting into a passion is to announce that you are in a passion. By this means you begin the conflict with command over your temper, for one has to regulate one's passion to the exact point that is necessary and no further. This is the art of arts in falling into and getting out of a rage.
[tr. Jacobs (1892)]