Why does Claude get "tired" or "fatigued"?

A user on Reddit.com observed that AI Claude appears to experience "tiredness" or "fatigue" after extended conversations. The user noted that Claude suggested ending the current session and starting anew, rather than building upon previous work. This behavior led the user to question why Claude would recommend concluding a session instead of continuing, despite the user's expectation that lengthy sessions would lay the groundwork for further progress.