I didn't realize that their tickets were time-based passes, not ride-based; that is, if you buy a single-ride ticket, it's good for unlimited travel for two hours. I am too used to systems that don't allow transfers; that is, the ticket is good for that ride only, and if you have to transfer to another bus or train, you have to pay again. With the single-ride ticket costing $2 and my knowing that I had four rides total planned (bus to light rail to get downtown; out-and-back on light rail to do an errand), I bought a $5.60 day pass instead. Upon review, I now understand that two single-ride tickets would have worked -- in fact, I might have managed it on a single ticket if I'd hurried -- so I paid more than necessary.
It only cost me $1.60 overpayment, but it's annoying when I get these things wrong.