a poor craftsman blames his tools
If someone performs a job or task poorly or unsuccessfully, he or she will usually lay the blame on the quality of his or her equipment, or other such external factors, rather than take responsibility for his or her own failure. After John spent all day assembling his new desk only to discover it was lopsided, he immediately declared that the package must have contained the wrong pieces. His wife replied, "only poor craftsmen blame their tools, dear."