As you say, its a matter of luck, being in the right place at the right time. I've reduced that by limiting myself to one place, so I reckon on that basis alone that I'm down to 25% chance.
Considering that most days I have a pretty limited window of opportunity as far as time is concerned, about an hour in the morning before work, and about 20 minutes after I get home and before it gets too dark, we're down to about 1% chance.
Which is quite close to being a certainty.
You can tell I'm a statistician by trade, can't you.