What your favorite teaching of Stoicism?

Stoicism has three key disciplines: Discipline of Desire, Discipline of Action, and Discipline of Assent. The Discipline of Assent focuses on approaching life with clarity -- your choices, opinions, desires and aversions rest with you. I find this is particularly helpful in staying focused on the here and now and avoiding negative thoughts. This allows me to focus only on what I can control and stay present.