In my opinion, for a lot of things such as the hard sciences, the nightly dreams of an individual, and matters of religion, there can be only one version of the truth. There has to be some ultimate truth which is always true regardless of a person's personal perspective. Even if you've been incorrectly taught the sky is green or you're color blind and see the sky as brown, the truth is the sky is blue. There are times the sky appears to be some other color, like at sunset when the moisture in the air reflects the sun and makes the sky look red or when there's smoke in the air and we say the sky is grey, but the fact remains the sky IS blue. Anyone who has ever studied philosophy will be able to put forth convincing evidence against what I just said, but I'm not looking for a philosophical debate.
      When it comes to solving crimes, there can be multiple versions of the truth and it's a detective's job to filter through all of the versions and find the version which is the ultimate truth. Why are there so many versions, yet only one which can be true? Personal perspective, lying to stay out of trouble, wanting to make the other person look guilty, and trying to cover up your own part in the situation all lead to multiple "truths". If a detective interviews three witnesses, they may get three similar but somewhat conflicting stories. If one saw the action from right beside the crime, one from across the street and behind the crime, and the other from a third story window above the crime, all three people will see some things but miss others. The detective's job is to put the pieces together to make a complete picture and reveal what really happened.
      A good example of multiple "truths" and only one ultimate truth is listening to what is said by two men who've been arrested for killing an elderly woman. One guy tells the story that he was there in the house with his buddy, but he stabbed the woman. Then talk to the second man and he says the same thing, he was there but it was his buddy who killed the woman. Both of these men are telling their version of the truth. One or both of them could be lying. The only thing a detective knows at the beginning is a woman is dead, which is an ultimate truth. It can be inferred from eyewitness testimony that one or both of the men are guilty; however, the witness could be making it all up, lying to get even with two men, or lying to cover up the fact they themselves committed the murder. Only the evidence can lead to the ultimate truth. When all the evidence is processed, the detective can separate the truth from the lies and determine who the murderer is ... one or both of the suspects or, possibly, someone else.
      There's really no middle ground for the truth, there's only what's not the truth and the truth. You're not an optimist for thinking it true a glass is half full or a pessimist for thinking it true it's half empty. Even if you don't see the action itself and only the glass, the truth lies in the surrounding action. If someone is drinking from the glass, the truth is it's half empty. If someone is filling the glass and gets interrupted, the truth is it's half full.
      When you get stuck in the middle of someone's argument about who did or didn't do something, you may get one person's view of the truth and then talk to the other person and get their version of the truth. In this case, the truth may lay somewhere in the middle. In a murder investigation, a detective listens to many versions of what happened and then have to figure out what the real, ultimate truth is and make an arrest.