What do the pickups show and why are they sometimes negative?

Outcome vs Historical

For future dates, the pickup column displays the difference between on the books/Revenue driver and the last saved Live forecast. In the pickup column, you can revise or adjust how many rooms/covers/revenue you expect to end up with each day, plus or minus, compared to on the books/revenue driver.

Historical dates display the difference between the actual outcome and last saved Live Forecast. A negative pickup for historical dates tells us how much we missed compared to what we achieved this day. If we have a positive pickup, we ended up with more than we expected.