Thanks a lot:)

Let me use them both in a conversation: Two friends watch a very beautiful girl leave the building they are in. "Do you think we'll ever see her again?" "Don't bet on it." Meaning it is very unlikely. 2. "Do you think I could fly like Superman?" "No, it's impossible." Meaning it will never happen.

Don't bet on it means implies that the speaker thinks it is very unlikely. Although it may be possible, it isn't worth risking anything over.