Zuo 左: in its ordinary meaning ‘the left side’, but already on oracle bones used as a loan for zuo 佐, ‘to assist, to help’. and you 佑, ‘to assist, to protect’. The 漢語大詞典 says, ‘用兵則居次方位’: ‘in military operations it is the second position’. When you station an army ‘at the left’ you do not want it to attack directly, you only want it to support and protect the attacking division.
Ci 次: to station troops (軍隊駐扎).
The army is stationed at the left (the assisting/protecting side).
No curse from the ancestors.