Molecular errors refer to mistakes made at the molecular level in cells, including, for example, misfolding of RNA or protein molecules, misincorporation of amino acids in protein synthesis, and misinteraction between biomolecules. I argue that many genome-scale patterns in molecular biology and evolution (e.g., on transcription/translation initiation site variation, alternative polyadenylation, posttranscriptional modification, chromosomal locations of genes, and protein evolutionary rate) originate from molecular errors and differential natural selection mitigating these errors. Realizing that the cellular life is far from the orderly and harmonious picture commonly portrayed is important for understanding biology.