Rob/PA explained this to me in the best way I've heard, yet.

He gave me this analogy.......a skunk that we know is in the area.....

When the skunk's scent is very strong....we go on high alert. We know he's in the immediate area. When we smell the faint smell of a skunk.....we are aware he's "near"....but we're less concerned.

This is what we try to achieve with our scent control as hunters. We try to fool the deer into thinking we're not an immediate threat to him. Does he still know we're "near"? Possibly....and quite probably. Does he feel we're an immediate threat? Hopefully.....if we're playing the wind to our best abilities....and practicing a sound scent control regimen......he doesn't.

We just have to stack the odds in our favor as best we can.....and....roll the dice. Everyone's comfort level with that roll is different. Every deers' is, also.