I am not sure Japan had a strategy, as exemplified by a coherent assessments of risks and rewards, and most importantly, a plan to force the US out of the war. Rather it decided it was going to expand and had had a good measure of success to date fighting China and taking over Korea.
The Japanese military had not fought a real war with a peer military for centuries - discounting the massive incompetence of Russia in 1905. Quagmire as it was, China had a limited capacity to do more than static defense or waging guerilla warfare - Japan could always disengage from it. Inter-service rivalry was also massively dysfunctional.
So Japan in 41 is looking at the following facts:
China is not going well, but it's the Army's show.
USSR is too much to handle after Khalkin Gol in 39. Also Army's fail.
They don't have the oil to fuel their fleet and the US is pressuring them to leave China alone by not selling them oil.
Europeans colonies nearby have resources and their owners are busy with Germany.
Unlike today's 1-3 ratio, Japan's population was at 73M to the US's 132M in 1940 and the US military did not have the recognition it has today.
Shattered Sword claims, without going into details, that while Yamamoto might have warned about the US's industrial capacity, IF there a war then he was a proponent of ALSO attacking the US alongside with the Dutch, English and French colonies.
Another strand of the military establishment instead argued that they could take over oil producing regions like Java while staying well away from the US which would not fight so far from home without a good reason.
Yamamoto and the attack-the-US group won that argument. With that they made the following miscalculations:
kill enough Americans and they will back out.
unlike the Japanese code of honor the US is weak-willed and isolationist.
our military is supremely competent and will win by offensive power and fighting spirit.
After an initial highly successful attack Japan would:
fight a high seas battle using super-battleships like the Yamato to take out the US Navy
consolidate defenses on islands far away that would force the US to mount very costly invasions till they gave up and went home. (by 44 and 45, that thinking had, by necessity, shifted over to making the home islands un-invadable except by totally unacceptable losses).
last but not least, the distances in the Pacific are huge. That must have, reasonably, seemed like deterrent to determined US operations.
You could say that Japan was planning to get to a stalemate by a strategy of pure defense, albeit with tactical offensives, and killing enough Americans, after having secured enough advantage by its early offensive. Having captured Indonesia's oil fields it could develop its economy without being held hostage by the US.
This type of win-by-bodycount thinking would, in most cases, be laughed at by Western military thinkers (well, except for Westmoreland in Vietnam).
Yes, sometimes conventional wars are won just by inflicting massive casualties, as other answers have pointed out. But that is very much the exception.
Remember, the Japanese supreme high command, for all its militaristic dominance, had not fought peer opponents in centuries. Aside from the attempted Mongol invasions, Japan's wars had almost always been internal, except for a foray into Korea in the 1590s. Even internal warfare had largely ceased after the Tokugawa takeover. And whatever setbacks they had encountered were the Army's fault, not the Navy's.
The core problem was that Japan never had a credible way to knock out the US, only to make this a painful war. Once started, the initiative was to the US to fight on or to back down.
In short, arrogance and early successes made them hubristic and they miscalculated.