If you do something lest something unpleasant should happen, you do it to try to prevent the unpleasant thing from happening.
in case
I was afraid to open the door lest he should follow me.
我当时害怕开门,生怕他跟踪我。
And, lest we forget, Einstein wrote his most influential papers while working as a clerk.
而且,我们不应该忘记的是,爱因斯坦在做小职员的时候写了他最有影响的论文。