It means you should never rely on only one plan - in case it goes wrong.

这句话的意思是你不应该依赖唯一的计划——万一出错。

youdao

Since we only take one step at a time, there is no need to plan our route for one can make continuous decisions about where to turn next.

既然我们一次只走一步，就没有必要计划我们的路线，因为一个人可以不断地决定下一步去哪里。

youdao

If you only plan on capturing metrics for one or two projects, don't bother with this approach.

如果您仅仅计划为一两个项目获取度量，那就不必要用这种方法来费心。

youdao

In his speech Wednesday night, President Obama said the idea is only one part of his plan and should not be used as an excuse.

VOA: special.2009.09.12

Yet when one considers the need for affordable energy to power our homes and light our factories, only one plan stands a greater chance of success of securing our energy future.

FORBES: Which Candidate's Energy Plan is Better for America?

Forbes only offers one health plan.

FORBES: What's Going On During Open Enrollment At Your Company?

Worse, employers would only have access to one plan, vs. the wide array at the Massachusetts Connector.

FORBES: The Future Of Universal Health Care