Perhaps you've heard the phrase "Doubting Thomas". This comes from the Bible and is a reference to the Apostle Thomas. For full context, it comes out of the Gospel of John, chapter 20 verses 24-29, which are as follows:

Jesus Appears to Thomas
Now Thomas (also known as Didymus), one of the Twelve, was not with the disciples when Jesus came. So the other disciples told him, “We have seen the Lord!”

But he said to them, “Unless I see the nail marks in his hands and put my finger where the nails were, and put my hand into his side, I will not believe.”

A week later his disciples were in the house again, and Thomas was with them. Though the doors were locked, Jesus came and stood among them and said, “Peace be with you!” Then he said to Thomas, “Put your finger here; see my hands. Reach out your hand and put it into my side. Stop doubting and believe.”

Thomas said to him, “My Lord and my God!”

Then Jesus told him, “Because you have seen me, you have believed; blessed are those who have not seen and yet have believed.”

Thomas does not believe until he is given proof. He is not the type of person that runs on faith (faith being belief without empirical proof). If you want him to believe something is real or true, you have to show him it is real or true. And, of course, Jesus points out that it's better to believe without proof.

There are all sorts of clever theologians who try to make faith into a sort of logical debate. Without the type of proof a scientist would want, they must instead argue based on other factors that would instead act as weight towards the existences of God and Jesus and why the Christian view is the correct one. These arguments can work for many different types of doubting Thomases, but they'll still fall short for anyone that wants actual evidence.

It's hard for me to have that sort of trusting faith. Too many times I've had promises broken or seen people I thought were good turn out to be whited sepulchers--hypocrites that seem holy and good outside but who are full of vileness inside.

Knowledge is also a burden on belief. That the Old Testament comes not just from the Torah but from oral reports. That the whole Bible is an anthology written by different authors over countless centuries. The Bible Truth, as it were, seems itself to be a fiction. We're supposed to believe the Bible is the Word of God and thus True in all senses. This, you may guess, is where Bible literalists come in. If the Bible is True then everything in it must be True as Written--in other words everything must be literally true. This won't work. The first two chapters of Genesis show different creations. It's not very hard to find other narrative variations or even things (like the Flood) that won't work with a scientific understanding of Earth at all.

Now, an easier argument is a metaphorical truth. This doesn't expect someone to believe something is literally true that can be disproven by science, but rather that the Bible can act as a moral guide. However, even this won't really work. There are slaves in the Bible and slavery is never condemned in it. Indeed, the Bible was sometimes used to condone holding slaves here in the US. And, folks will be quick to point out, also used to condemn it.

In other words the Bible, like any book, is open to interpretation. Those who want can use anything in it to be able to justify any position they want and this will be (in their minds) as valid (or more valid) than someone doing it for some other position that they disagree with. I'm not sure how I'm supposed to have a firm faith through the Bible with these sort of lexical shenanigans.

Even worse is knowing the text of the Bible. It's very clear in a number of places that not everyone will be saved. In fact, the path to salvation is supposed to be very narrow indeed. Yet my sense of justice, human as it is, rebels at such a thing. A mass murderer that comes to believe may be saved and go to heaven at the last minute, yet an atheist that save millions of lives will go to Hell for the crime of not believing! Imagine being in Heaven alone because your friends and loved ones are all in Hell!

So I have a hard time believing, of having real faith. I don't know if God is real or not, of if God is real what sort of God there is. I have a hard time with faith when there's no proof or the type of proof I'm supposed to accept are arguments that can be debated.