Fact and Opinion?

Fact is a word that is used or implied to a particular situation that exists.

Opinion is a feeling or thoughts about somebody/something, rather than a fact.

Take an example, X and Y work under the same company. X feels that Y will put X's career in danger. Therefore, X did something to prevent Y before Y has the chance to do so. Now this "did something" is very general and can be anything. Let me just name that something as setting up a plan to end Y's career in that company before Y can put X's career in danger.

One day, X successfully accomplished what he had planned and Y was fired by the company.

As a reader of this situation, how would you judge the act of X? Should X do what he did to stop Y before Y can do what X feels that Y will do to X that will put X in danger?

The fact is X did something to get rid of Y from that company. However, what X feels is merely an opinion that isn't a fact yet. That is to say, what X felt might not be true at all. X might be wrong but X just does not like it to be true.

From here, how should human handle this type of problem? Should we act on fact or on opinion? Should X wait until Y actually did what X felt before X do something on it? Is it too late to take action if we wait for something to become a fact?

Note: Do not limit it to just the above situation where the outcome is bad. As a yin-and-yan believer, I feel that sometime we should act based on fact and sometime we should act based on opinion. The question is "When to act based on fact and when to act based on opinion"?

Any idea?? I am sorry if it doesn't come out clear to you. =)