We've all got a bit distracted and ended up being late for something, but imagine if your daydreaming cost you a place in two Olympic events.
That's what happened to 26-year-old British swimmer Melanie Marshall.
She wasn't in the right place when her 100m final was called at the British Championships in Sheffield.
The slip-up means she has been disqualified from competing in the 100m freestyle, and probably the 100m relay as well, at the big event in China.
"I was five minutes late. It's my own responsibility," said Melanie.
Swimmers are meant to gather in a special room 15 minutes before their race. When Melanie didn't show up on time, she was banned from taking part.
Lucky
Luckily, swimming experts say Mel's strongest event is the 200m freestyle and she's still all set to take part in that, and she's got the chance to make the 200m relay team too.
Scotland's Caitlin McClatchey won the 100m final and booked her place at the Olympics.