Dangers of disbelief

I wonder if one can sabotage ones relationship in its fullest potential because he or she does not believe the whispers they hear from the Holy Spirit. Or maybe they don't believe the blatant miracles set before them chalking it up to coincidence. The Biblical examples I have for now are in Numbers 13 and 14 when the 12 representatives from Israel went into the land God promised them to check it out. Ten of the men were totally intimidated and 2 were ready to go into battle believing that the Lord would go before them. Because of the 10 unbelievers they whole of Israel were sentenced to wonder the dessert for 40 years. Not without God, but they could have just gone into the promise land and not the dessert. THEN! When God told Moses to speak to the rock and instead he struck the rock, God said, "Because you did not trust me enough to demonstrate my holiness to the people of Israel, you will not lead them into the land I am giving them!" (and it seems Aaron was also taken down with him in this scenario, we don't know the whole story really as far as Aaron's attitude and actions.) Also Zachariah went mute when he didn't believe right away when the Lord said he would be a father. I'm just wondering how many times we miss something amazing from God just by not believing.