Awitness on the stand swears that he saw someone commit a crime. must you believe that the testimony is valid when a witness testifies so forcefully?

If a witness on the stand swears that he saw someone commit a crime, and they testify so forcefully, the answer as to whether you must believe that the testimony is valid is the following one:
No, because there is a great possibility of a "false positive" identification.
This means that this person thinks they are 100% sure they know who committed this crime, when in fact, they may not be correct and may be wrong in the end.