Why was programming in machine language difficult and unreliable?

Programming in machine language is difficult and unreliable primarily because it requires a programmer to manage every idiosyncratic feature of a computer's data storage and operation. Because machine language consists of numeric codes—strings of 0s and 1s—it does not resemble human language or conventional mathematical notation, making it highly unintuitive to read and write.123

Furthermore, machine language is not portable; its specific vocabulary and syntax are dictated by the physical and logical structure of a particular computer architecture, meaning codes vary from one machine to another. This high level of detail forces programmers to possess deep, expert-level knowledge of the hardware. Because the language is so far removed from the way problems are naturally formulated, it is prone to human error and difficult to debug. To mitigate these challenges, early programmers often used intermediate, paper-and-pencil methods to organize logical structures before manually translating them into machine code.23