to throw oneself wholeheartedly and suddenly into an activity or state

one-sided enthusiasm (short for [[剃头挑子一头热|剃頭挑子一頭熱|ti4 tou2 tiao1 zi5 yi1 tou2 re4]])

to be completely baffled or at a loss to understand a situation

one-sided enthusiasm where only one party is interested or motivated while the other remains indifferent