Unbelief and unbelieving believer hinder the blessing of God.
Striking the rock did not keep Moses from the promised land. It was rather his repeated inability to speak to his circumstances (Mark 11:23) and people under his authority, as Moses' tendency was to give ear to the people and murmur and complain about them to God as they murmured and complained to him. Joshua and Caleb did not allow the people to be their point of reference, choosing rather to believe the Word of the Lord and boldly do what God said.
'And the LORD spake unto Moses and Aaron, Because ye BELIEVED ME NOT, to sanctify Me in the eyes of the children of Israel, therefore ye shall not bring this congregation into the land which I have given them' (Numbers 20:12). 'Be ye angry, and sin not' (Ephesians 4:26a). Since righteousness is by faith (Romans 1:17), the evil that kept Moses out of the promised land was unbelief (Hebrews 3:12).
Beware of unbelieving believers and ministers who don't believe their own prayers will be answered (Luke 1:18-20, Hebrews 11:6). Thankfully sometimes God shuts His preachers' mouths to fulfill and answer their prayers (see also Numbers 14:28).