Latin root sist means stand
Comes from Latin sistere, the second-person singular future passive indicative of sisto means stand.
Stand can be aggressive when it's done actively, because it's a fighting stance, when it's done passively, it means hold, keep, remain.
Another root tain has the similar meaning, tain means to hold, the difference is you hold with your hands, but stand with your legs. For example the retain and resist, retain is to keep something to not to be affected, think about grab something back, there is no aggresiveness here, but when you resist, you are doing almost the same thing as retain, but in a more aggresive way, you stand for fighting back. Notice the two backs here have different direction, in retain, the back is this side, in resist, the back is the opposite side.
Stand(sist) upon(in), means declare something strongly. What is the instinct action you will do when you want to defend your view point in an arguing or to assert the ownership of something like property in conflict? Of course it should be standing up, the stance is an aggressive signal, telling others you are preparing for fight to defend the things you are insisting.
Stand(sist) together(con), means a thing is composed of it's members or ingredients. A month consists of four weeks. A year consists of twelve months. A fiscal year consists of four fiscal quarters.
Almost anything can be divided to small parts, even the atom can be divided, there is this simple relationship between the thing itself and the parts made it, when this word is used, it usually means a simple relationship in which the parts are clearly separated, and nothing more are involved, unlike compose or made of which involves some complex processes. For example, a year is made of four quarters is not very appropriate because there is nothing more needed to make, the four quarters just simply ranged together is enough to be a year. You can say water is made of oxgen and hydrogen, because there are extra processes to make it, you can not get water by simply putting oxgen and hydrogen together, they need to burn and then becomes water.