게 미치다

be crazy; or affect something

Two very different uses share the verb. The casual one is being crazy, used as praise or shock: temperatures that insane, a share price that went mad, sweets that are not even that sweet, someone described as quietly unhinged in a good way. The set phrase 미친 듯이 works as an intensifier meaning like crazy. The formal one is exerting influence on something, which is what the line about which factor had the biggest effect means.

Register: the crazy use is casual, the influence use formal