It makes you realise that we aren't all perfect and it could all end in a split second. Just as it can in the car on the way to the airport.
I've had a few close ones....
Worst one was downwind in the circuit and a stray aircraft came from the opposite direction, almost the same height from left to right. Never saw it coming. If I'd had an aerial on the roof he would have hit it.
Another one, was climbing out after takeoff and said to the passenger, "I'll just lower the nose every few hundred feet to look around for aircraft" Pushed the nose forward to see someone coming almost head on (hidden behind the pillar).
Next worse, was flying with some aircraft on a fly-away. Mate did a radio call and to be funny said "4.2 miles" or similar... looked at the GPS and so was I.... he was hiding behind my pillar again. Those pesky pillars!