Why were we in Vietnam?
Why did we stay in Afghanistan for so long?
The military industrial complex does indeed find war funny. It's called laughing all the way to the bank.
This is why many want cooler heads to prevail in the Russia-Ukraine war now!
Those who have lived through war know how horrific and uncontrollable it is and how sociopathic you need to become to wage it successfully.
Intelligence is the first problem. Then the model to fit it to. Then the conclusions to take from it. Each layer is HIGHLY prone to error.
Just an example: precision munitions largely eliminate the odds of NOT killing to zero but then it's the intelligence and interpretation that becomes the weak link: are you really hitting the right target for the larger purpose, or are you doing everything wrong hitting the wrong target because you are measuring success wrongly (e.g. body count - as we did in Vietnam and then returned to in Iraq and Afghanistan - simply because it was the only thing we could measure; classic "streetlight fallacy")
I would argue Russia is in a very similar position today, and if we don't act decisively now, we're just enabling Putin to do far more damage in the long run. The risk of WWIII and a nuclear exchange does exist, but the risk of on inaction is just as high.