How can anyone who hasn't realised the truth, claim that Mahatma Buddha or any other person in history realised God or the Truth?

Isn't it possible that whatever they have realised is just a psychological effect? Doing continuously hard practices leads to affect their mind and they tend to believe that, yes, this is the truth. They started lying to themselves that they know the truth? **I truly respect their teachings which shows us the path to live a good life. I am just talking about the real truth (if there is any).** With love.