柯 is formed by two parts: 木 wood and 可 may. In 5 xing, 木 represents stability, growth (at top), therefore it is 可 possible (to win).

Jacob said,      @shubert You do realize that there are dictionaries in Chinese, right? Some of these dictionaries would include entries for 柯 that have absolutely nothing to do with your fantasy definition and etymology of the character. I'm sure you also know that the vast majority of characters include phonetic elements, e.g. 柯