It's not clear from the sentence itself. The context would make it clear.
The person tried -- that is, made an effort. Normally, if nothing else is said, we assume the person didn't succeed in the ultimate goal of making the boss understand, otherwise the sentence would have been "I talked to my boss..." Or it might have been: "I tried talking to my boss... and believe it or not, it worked!" Then the context makes it clear that the person did succeed.