Somewhere on his blog, Scott Adams (of Dilbert fame) lists things he used to believe, sorted by how old he was when he realised they weren't true. Here's my version.
03: Adults know that children can see them.
04: Once you understand there's no reason to be afraid, fear vanishes.
05: Talking to yourself means you're mad.
06: My teacher knows what she's talking about.
07: Violence achieves nothing.
08: People appreciate honesty.
09: Nobody wants to be an outsider.
10: People are basically decent.
11: You can't gain real understanding from books.
12: True friendship is unconditional.
13: People know why they believe what they believe.
14: People can be persuaded with simple facts.
15: Being able to spell correctly and use big words makes you intelligent.
16: The official rules are the real rules.
17: There are two sides to every story.
18: Elegant ideas are truer than ugly ones.
19: Everyone realises you can't trust the police.
20: Being a parent makes you competent to raise children.
21: Money doesn't make you happy.
22: It's possible to be apolitical.
23: Drug users are damaged victims.
24: Once you know what's right, doing it is easy.
25: Overweight people are ignorant about health.
26: If someone loves you, they respect you.
27: You can repair psychological damage with kindness.
28: Losing faith means gaining reason.
29: The young are rebellious and the old are conservative.
30: Doing something for a long time makes you good at it.
31: You can't love humanity without loving humans.
32: Respecting a person means respecting their beliefs.
33: Everyone grows up eventually.
34: Memory is accurate and willpower is strong.
35: Only love that lasts is genuine.
36: The purpose of schools is education.
37: Science is the search for truth.
38: It's impossible to be mistaken about you own beliefs
39: Ruthless people are sadists.
40: Pleasure is sinful.
41: Reason has a method and unreason has none.
42: Doing what you love means doing it well.