Are our lives completely predetermined?

[Squeek]

No.

If people just went 'well my life is predetermined so who cares what i do' then nobody would ever do anything, ever.

Believing in predetermined life, to me, is like admitting the reason why you failed at life. "I was destined to fail. You can't blame me." Of course, it could also lead to success, but failure is so much easier to talk about since that's generally how these things come about in the first place.