insist on = demand or request in a very firm way. Demand: (He insists on talking to the manager about the problem, and refuses to deal with any of the employees.) Request firmly: (He insisted on paying the restaurant bill for all of us even though it was a lot of money.) persist in = to keep on doing something, despite difficulty or opposition. (He persists in trying to win her heart, even though she doesn't even know that he's alive.) 1. stick to = to adhere to, physically speaking (If you put some glue on this paper, it will stick to the wall.) 2. stick to = to continue to do something faithfully (That cake is very tempting, but I am sticking to my diet because I really need to lose weight.) 3. stick to = to be faithful to an idea or principle (He doesn't care what people think of him, he's sticking to his opinion on the subject.) Hope that helps.

insist = it's like "demand" or "require". often if you try to do something nice for someone, and they refuse politely, you can say "no, I insist! (you must accept my favor!) " ... it can mean other things too, like 愣說。。 非要 persist ＝堅持 stick to = 堅守