This quote is saying that if you frequently accept and believe lies, you will start to lose trust in other people and will only be able to rely on yourself. This is because when you believe fraudulent information, you can no longer trust the sources that gave you that information, which is why it is important to be able to discern when something is a lie and to not accept it. Ultimately, you should always trust yourself because you know yourself best and have your own judgement to inform your decisions.