simplified point of view

external:
0% - pure pessimism - person believes that the universe is their enemy and everything happens exactly opposed as to what they want
100% - pure optimism - person believes they are in charge of the universe and everything happens exactly the way they want

internal:
0% - person believes that he is capable of nothing and can't do anything right
100% - person believes that he is capable of doing right anything, anywhere, anytime

balance:
0% - person believes that external factors will decide the final outcome no matter what
100% - person believes that he can always overcome external factors with his actions

'external' consists of all external factors that influence the person's actions.
'internal' consists of all personal factors that influence the person's actions.