Why are we surrounded by idiots and why are looks deceiving?

I feel like a 5 grader, naive kid who learns first lessons in life like...never borrow your expensive things or...never believe what people tell you...

In fact few years back I had meet a person who was (what word shall I use?!?) and was lying to me for every possible thing...seems I have forgotten my lesson

Now it makes me think. Am I stupid for allowing similar mistakes to happen or am I just an optimist.I would like to believe that it is the second option but as people say it's not bad to make mistakes but it's bad to repeat them. Excuse my lame translation:)

Story 1

I borrowed my bike to a girl I know. Few days later it turns out that she and her boyfriend are having some drama. He is keeping the bike and threatening her with throwing it away. She is telling me she'd rather buy me a new one than talk to him.
My side to the story 'it costs xxxx czk, if they have pink it's fine by me'.
Well, not really. I do a favor by borrowing my bike and what I get back is some drama and concern I might not get it back.
Lesson learned...never ever borrow something valuable which you are not ready to loose. The thought of loosing almost half of my salary, understand the bike, was making me unhappy.
P.S. I got my bike back but I still don't get why I got involved in this story...

Story 2

I had mentioned that it is a wedding season. This Saturday I am going to the first of three weddings. I was casually chatting with a guy I met on the hen party of bride to be. Reason for me chatting to him was that he was to Hochkar one week ago and I was inquiring about the snow conditions etc. After I came back I felt like bragging how it has been there. From word to word we came to speak about the bride to be and then he said 'oh, how will I get myself to the wedding' ...So I asked him if he had an invitation and after he had answered positively I offered him a ride.
Luckily this piece of information had reached the bride to be on time when I found out from her that he is actually not invited.
Consequence to his lie was me asking him again if he is sure he had invitation to which he answered 'yeah but not an email or sth just verbal invitation'...
I said that unfortunately there is no space in the care available and ended our conversation.

I am curious what will be tomorrow.Those two stories above in my opinion are demonstration of being punished for offering help.
On the other hand if we shut ourselves down and don't let anyone in or close we would also get rejected...so what's the conclusion? Anyone?