Explain how geographic isolation can lead to allopatric speciation

i believe that if you say you can, you cant and if you say you can't your right. i believe i can do anything i set my mind to. i've applied this with my everyday life. it me get motivated to do stuff.for example, i apply this to do school. if i believe i can finish a whole class in a couple of week's i will be motivated to do the class until i finish it, and if i believe i can't, i will get distracted and do other stuff besides doing my work. it changed me by believing i can accomplish anything i set my mind to.