This is a sentence that is used to describe something that needs a lot of attention to detail.  It means to be thorough.

別忽略了細節。

有時，連最微小之處都得留意，以免「因小失大」釀成錯誤。原句中的 i’s 和 t’s 代表要「加上」或「刪除」那小小一撇，都是學問；應一絲不苟、重視細節才是。