A closer look
Was is the past tense of be, not present tense. The present forms are am, is, and are. So Yesterday I was tired but Today I am tired.
The same sentence, then and now
Yesterday the sentence was She was at work. Today you would say She is at work. The only change is the verb: was points back in time, is points to now.
Compare I was hungry an hour ago with I am hungry now. Same person, same feeling, only the time has moved.
Was or were
One near miss: was only fits singular subjects in the past, I, he, she, or it. If the subject is you, we, or they, the past form is were: They were late, not they was late.
The trap is you, since it takes were even for one person: You were right is correct, even when talking to a single friend.