Once you get more than one person writing it, it's very easy for any two programmers to overwrite each other's work if they're working on the same file, or to send incompatible instructions that simply causes the computer to choke, and this problem grows larger the more programmers are involved.
１人で書く場合でもそうですが 書く人間が複数になると 同じファイルをいじる２人が 互いに上書きしたり 矛盾した命令を送って コンピュータを 立ち往生させる ことになりやすく 関わるプログラマの数が 増えるほど