Unbelief starts with a question. And expands into more questions. And as those questions go unanswered or not answered well enough, that is when unbelief sets in.
Many Christians try to ignore the questions they face because often times Christians will treat doubt as a sin and make the one questioning feel shame and this can actually weaken one's faith in the long run.
Some will simply not seek answers because they're afraid the answers they get may not be what they want to hear. So they ignore them in hopes they will just go away.
And yes, there are some that don't get satisfactory answers. This may be because those around them have poor teaching and theology, or that the doubter demands such detail in the answers they seek they make it impossible to be satisfied.
All of these will eventually lead to unbelief. There is a source for your unbelief, but you have to look internally to find what that is. Then deal with it directly. If not you will continue down the road you're on.
After Jesus was crucified the reports spread that he had been risen. Thomas didn't believe they were true (he was dubbed Doubting Thomas), yet when Jesus came to him, knowing his doubt, he was not rejected.
John 20
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.”
26 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!” 27 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.”
28 Thomas said to him, “My Lord and my God!”
29 Then Jesus told him, “Because you have seen me, you have believed; blessed are those who have not seen and yet have believed.”