I don't understand how people view changing the past with time travel. If I go back in time I might experience a given point in time twice, but that point in ti

I don't understand how people view changing the past with time travel. If I go back in time I might experience a given point in time twice, but that point in time still only happens once. So if I go back to 1940 and kill my grandfather, then the first time 1940 happened he got shot. The second time...there is not second time. (Fortunately my parents were born in 1930s.)