I am going to answer this question in two ways that is, the religious way and those that do not believe in religious stuff. For those that do not believe in religious stuff, having faith in people is impossible but more of hope or trust in people is. Because, the definition of faith according to the Oxford Dictionary, is complete trust or confidence in someone. Some time back, having faith in people was possible but now even confiding in people, can bring you problems which can greatly affect one's life because the evil in the world currently, is just too much. For such people, before they have faith in someone or something, they must see some positive signals. And these are the people that believe in the common saying "Seeing is Believing". If having faith in someone or something was easy for them, they would not wait to see positive signals before having faith in that someone or something but rather, they would just have faith in that someone o something without seeing any signs.
In the religious sense, I will explain it from the Christian's point of view. In the Holy Bible, according to Hebrews 11:1, Faith is the substance of things hoped for, the evidence of things not seen. This statement contradicts the regular statement, "Seeing is Believing". This means that you believe in something or someone without seeing any signs. For example, We us Christians, believe that there is a God. But no one on this earth, has seen God. I know you will probably say Moses but he only saw His back. Even though we have not seen him, we still believe in Him or in better terms, have faith in Him. Having Faith in God when everything in your life is going well is easy but when things in your life take the other turn, having faith in God becomes very difficult. To conclude, actually, a person of faith or a man of faith is someone that believes that God will turn things around even though everything in his or her life is not going great. A great example of a man of faith in the Bible is Abram whose name was later changed to Abraham. God told Abram to leave his country, his family, his father's house when he was 75 years old. Now bear in mind that, in those days, man lived on earth for a long time. So Abram along with his wife and nephew, not knowing how everything was going to play out, just obeyed God and left his country. But in the end, everything played out great. This is the true meaning of faith!!!! Faith is not easy but if you ask God for his divine strength and guidance, He would breakthrough for you beyond your imagination.