was so tired that I couldn'tA feminine speaker uses this pattern to express that she was unable to do something because she was very tired. The adjective and verbs change with the speaker and tense; for example, estaba tan cansado que no podía is used by a masculine speaker.
SP: Después del viaje, estaba tan cansada que no podía caminar.
EN: After the trip, I was so tired that I couldn't walk.