What events cause the monster in Frankenstein to change his attitude regarding the world around him?
There are multiple events, within Mary Shelley's Frankenstein, which cause the monster to change his attitude regarding the world around him.
When the monster first becomes aware of his surroundings he is afraid. The sunlight burns his eyes and the night brings cold. It is not until the monster beings to understand himself and his surroundings that he first begins to find hope.
Not long after, in his quest to find food and shelter, the monster comes across an old man in a hut. As the monster entered the hut, the old man flees (fearful of the monster). After leaving the hut the monster comes across a small village. The villagers here either run from him or attack him. Essentially, the monster's first meeting with humans is not positive.
One of the only positive experiences the monster has comes with his observation of the De Lacys--until he introduces himself to them. It is through his initial observations that the monster realizes what love is. Unfortunately, his hope to be loved by the family is destroyed given their utter fear of him.
Over the course of the novel, the monster is repeatedly chased, threatened, and harassed (he is even shot after rescuing a little girl from drowning). One could assume that the monster's brushes with humanity are anything but humane.
The monster is abandoned, isolated, and exiled. Society fails to accept him. Therefore, the monster's change in attitude comes form the fact that he is presumed to be monstrous and is hated for his differences. Initially, the monster had hope for his life. This was short lived given the negative way those around him reacted to his being.
The first part.. I answered on your other question... and I haven't read Lord Of The Flies but I will answer the other part :)
The changes that occur within 'Frankenstein' to the daemon reflect upon one's thoughts and ideas of the world as easily manipulative and something that is not set on stone. Although one's desires stay the same throughout life, through this novel it is demonstrated that a person's ways of going about dealing with their situation can change, particularly due to a change in environmental/external stimuli.