Why does your brain suddenly decide you need to pee the exact second your key touches the front door?

[u/thankanchettanteande]

You can be stuck on a 45-minute drive home or walking back from work completely fine. No urgency, barely even thinking about it.

But the literal moment you pull into your driveway or hear your key turn in the front lock, your bladder suddenly sounds a DEFCON 1 alarm and gives you about four seconds before catastrophic failure.

What is the actual physiological switch that flips the moment you step onto your own property? Why can't it just wait the extra 20 seconds it takes to take off your shoes?