The same hour can be spare time to one person and borrowed sleep to another.

The same hour can be surplus in one life and stolen from another, and nothing about the hour itself shows the difference. What makes it spare or borrowed is everything surrounding it: who else depends on you, what you gave up to be free at that moment, how much rest you had in reserve. People with generous margins tend to assume the margin is universal.

Before assuming someone can spare an evening, ask what it costs them rather than how long it takes. And when you find yourself resenting your own reluctance, check whether you are treating borrowed hours as though they were spare. The tiredness may be accurate reporting rather than a failure of willingness.