Yes luck is a big factor.
I was caught once by a copper timing me between 2 points from the top of a hill 1/4 mile away and then radioing his colleagues up the road to flag me down. No amount of awareness could have averted that, short of being psychic.
Also, you have to remember that whenever Sloper got stopped by the old bill, there was a bit of funny-handshake/trouser-leg lifting and an "on your way sir, I didn't see a thing...."