Some recent wars which grabbed wide-spread attention in the West had in common that political goals and even more so expectations were not met until after they became much, much more humble.
A common explanation for this until as far as I can tell a few years ago was that the Western military didn't take off the gloves, did not use full and if needed indiscriminate firepower. The theory was that restraint reduced Western military might to a degree that allowed the enemy to survive.
This thesis was apparently replaced by a greater understanding that violence sows more violence. Smarter warfare was widely thus considered to be necessary, exemplified by the COIN fashion.
That did fade away over time as well, though. More and more voices acknowledged that political goals aiming at changing alien countries to more preferred patterns were bound to fail because of stubborn regional traditions, customs and culture. This view basically asserts that you cannot convert a tribal society into a Western-style
civilisation democracy in a few years. It's still dominating the perceptions as far as I can tell.
Some people even go so far as to expect a "long" (open-ended) "war" of killing enemies without clear gain.
The people are missing the elephant in the room.
Disappointment in war is not a speciality of such wars, it is not dependent on unrealistic or overambitious goals.
Disappointment in war is the rule,
not the exception!
not the exception!
Warfare is about (at least) two parties warring, and it is NOT producing more than it destroys. At most one side can "win" a war unless there's a really unrealistic set of preferences at work (and then negotiations would clearly be preferable).
It is thus guaranteed that at the very least 50% of the parties in war will lose.
Now look at history.
History books are full of wars which ended unsatisfactorily not for one, but both (all) parties. A country going to war against another respectable country voluntarily and getting what it wanted is a rare occurrence.
This isn't only about mission creep; this is about a systematic overestimation of the probability of success and a systematic underestimation of the costs of warfare.
The people who lament about the trickiness of wars against elusive, "irregular" or "hybrid" or *enter fashionable word for poorly equipped yet tenacious opposition here* have a problem. Their problem is that they don't understand that they are not looking at exceptions. Maybe they are too clueless about history, having learnt only a caricature of history or only ridiculous details about their own nation's epochal wars (preferably victorious ones).
The reason doesn't matter much, for I am sure they won't detect their misunderstanding. They will cheer for the next stupid war, especially if they can talk themselves into believing that it will be different this time.
The military-industrial complex will happily provide fancy an fashionable theories and toys to cater to this apparent need of fooling oneself into believing that the next war may be successful.
I propose an alternative. Maybe it can provide you the desired peace of mind and satisfaction that the war-lover crowd never seems to have for long:
Let's not look at whether we're able to force distant foreigners into submission and dictate changes to their country. Let's instead look at whether we are safe from military aggressions in the classic sense. Can any foreign power fool itself into believing it could "win" by attacking us?
Think about it, then feel free to relax. You might get a great peace of mind and satisfaction this way, very much unlike the people who are being fooled by fearmongering, bogeymen propaganda and warmongering.