painful lessons的用法和样例：
例句
- Europe's plans for further unification may be up in the air, but people from Helsinki to Rome have been learning an often painful lesson in recent weeks about how entwined their economies have already become.
欧洲进一步统一的计划可以尚未定案，可是从赫尔辛基到罗马的人在最近几星期得到一个时常令人痛苦的教训：他们各国的经济已经如何地牵扯在一起了。
