Different people looking at same thing can see/feel different things. Or even you in different mood can see/feel different things looking at same item/person. For example: Its raining One can look and see mud, dirt, feel cold, windy Other can look and see rainbow in the sky, see bright colors of grass and leaves, feel fresh air with smell of rain or lets take some guy one can look at him and see just human, male, nobody for him other can see at him son, friend or love, someone special or enemy

We all might look at the same thing, but each person might take away or "see" different things, for whatever reasons. Some people are more positive than others. Some people may tend to notice negative things. We probably cannot notice every aspect or detail. So Thoreau is saying that what we notice is the important thing.

It means you were not judging on a scenario but on the happening of the scenario.