“It is of the Lord’s mercies that we are not consumed, because his compassions fail not. They are new every morning: great is thy faithfulness. The Lord is my portion, saith my soul; therefore will I hope in him.”
If we fill our thoughts and speech with contradictions and foolish words, then why would we expect God to believe what we say to Him? If we want our prayers to be acceptable to God, we need to obey what Jesus said, and we always should say what we mean and mean what we say.