In the work, Zeva’at HaRivash, the Baal Shem Tov states;
Shiviti-I have set God before me at all times.” (Psalms 16:8) Shiviti is an expression of hishtavut (equanimity): 1 no matter what happens, whether people praise or shame you, and so, too, with anything else, it is all the same to you. This applies likewise to any food: it is all the same to you whether you eat delicacies or other things. For [with this perspective] the yetzer hara is entirely removed from you. Whatever may happen, say that “it comes from [God], blessed be He, and if it is proper in His eyes…” 2 Your motives are altogether for the sake of Heaven, and as for yourself nothing makes any difference. This [sense of equanimity] is a very high level.
For the Baal Shem Tov, Shiviti is the notion of equanimity, which provides the means for allowing G-d to dwell within ourselves. When we are able to rise above ourselves, whether with something good or something bad, we nullify our being, humbling ourselves to a place were G-d then enters. Do we respond to praise and derision in the same manner?
For the Baal Shem Tov, equanimity is not just with regard to our character traits, the internal aspect of our lives, but it is also in the material, the external. Do we see everything in the world having equal value, were the most expensive item and the cheapest item are on equal footing. Shiviti is the ability to reach a place of absolute nullification in the eyes of G-d.