Hi, I would say when you believe in something it can only be strengthen with time. As long as you hold on to the conviction it either becomes real to you or it doesn't. For example, Jesus Christ said we can have faith that can move mountains or rather if you believe the impossible will happen.
So, you have to ask how strongly you believe in something. If it seems impossible, what fact can you make to help you feel stronger to convince yourself. Okay let me give you an example: The Bible tells Abraham all the families of the ground will "bless themselves" because you listened to my voice, Genesis 12:3. Now how is that prospect fulfilled during Abraham's lifetime? Well, no matter what was prophesied to Abraham he only had one son by another woman and not his wife even as God promises his wife will have a son. Everyday Abraham must build his faith and believe in the prophecy spoken by God. But with faith he can see the prophecy was obviously in the future.
Now we can understand that faith is built up through time using accurate knowledge. If God promised that Abraham would become a nation, he must believe only when he cannot see further than his grandson. God never expected Abraham to just simply believe suddenly without children. When he remarried to another wife, he also had children from that woman too. It must have been clear in Abraham's mind that when God gives out salvation to people, only those who have faith can bless "themselves" using the tools of salvation. So, the idea is only if you believe can you acquire salvation because it is a spiritual reward for those practicing faith in Jesus Christ. Food for thought Jesus Christ is showing us how to build faith, as you believed in Jesus believe in yourself the same way. At one time he tells someone "Let it happen according to your faith", Matthew 8:5-13. Peace.