all's fair in love and war(unpleasant behavior is acceptable during love and conflict) phrase [UK: ˈɒlz feə(r) ɪn ˈlʌv ənd wɔː(r)] [US: ˈɒlz ˈfer ɪn ˈlʌv ænd ˈwɔːr]
the end justifies the means(morally wrong actions are sometimes necessary) phrase [UK: ðə end ˈdʒʌ.stɪ.faɪz ðə miːnz] [US: ðə ˈend ˈdʒʌ.stə.ˌfaɪz ðə ˈmiːnz]