What do you mean it rains before opening an umbrella?

The expression "rain before opening an umbrella" is usually used to describe that someone or something is late or has already happened, but measures are still under consideration. It conveys a passive or procrastinating attitude, because you should get your umbrella ready before it rains, instead of waiting until it rains before deciding to open it. At this point, it is too late.

This expression can also be used to criticize someone's decision-making or action is not cautious or unpredictable, because they are not prepared in advance, but wait until the problem arises before taking action. It means to be prepared before things happen, not to wait until later to take countermeasures.

In a word, "rain before opening an umbrella" conveys a passive and careless attitude and emphasizes the importance of planning and preparation in advance.