He has been one for quite a long while when we meet him in his first recorded adventure. In that time there is very little he has not seen or done or heard and his experience is both a boon and a chain. While his years in the field causes him to suspect anybody and everbody, it also can blind him to the fact that a truth is a truth.
Many of those around him, and many more in the current Administration, wants to deal with things as black and white, this or that, Clark has learned to see in shades of gray. If asked, most of those who work with him would say Clark leans far more to the darker shades, finding bad in lots of things. His often sardonic outlook on life would back that up.
One example of that somewhat mocking attitude is his approach at places like the TSA security checkpoints at airports. "Ethan always loved to pull the CIA card on an unsuspecting lower-level law enforcement officer. Strictly speaking it was only reserved for need-to-know situations, but he used it loosely at times. Parking meter runs out? 'Official CIA business, you won't need to worry about filing that ticket officer.' The only ones that he hadn't done it to at some point were mall cops and he was convinced that if he had a kid - something that he vowed to never have - then he probably would have used it on a Black Friday to get the hot ticket item of the year."
"Just because you work for the world's pre-eminent spy organization doesn't mean that you can't have a sense of humor. It's what keeps us alive or at least sane" is another example of the attitude Clark takes with him. He finds, though, that a lot of the people he deals with either do not share his outlook or just do not get his humorous quips - mostly the latter.
Noteworthy comment:
"It always amused Ethan that baseball was one of the few professions where you could succeed thirty percent of the time and be considered a super star."