(Why) is it wrong to lie?

It's not always wrong. But it's wrong for a politician to lie because the interests of the nation are at stake.

Lying can be damaging to others and to yourself and your trustworthiness. The Bible says lying is wrong - God clearly knew lies can hurt people. Jesus said there are two important commandments; love God and love your neighbor. The 10 commandments are completely covered with just those two. If you're lying, you're not loving your neighbor and it's considered sin when it can hurt other people or goes against that command.

So JohnH, deceiving is another word for lying. Personal gain in itself is maybe not wrong. So is lying wrong? if so why?

You tell us why it is wrong to lie. You lie all the time, and you keep repeating your lies no matter how many times they are refuted.

Lying, means deliberately deceiving other people for your own gain

because eventually you will be so use to lying you won't know what's real anymore