Exactly.
One can analyse events from what was known at the time and or from what was known subsequently.
One can judge the ‘rightness’ of past actions only from the knowledge which the actors had at the time.
Bad historical judgments occur when people confuse what was known by the actors at the time with what is known subsequently.
A brilliant example of confusing past and present knowledge to produce outstandingly bad, indeed ridiculous, historical judgments comes from the Principal Historian at the Australian War memorial in a tenuous paper, which includes gems such as this about the Australian Prime Minister, John Curtin believing that Australia was still at risk of invasion during all of 1942:
What explains Curtin’s anxiety? Australian and Allied leaders in Australia
knew of the Japanese decision not to invade within a month of the debates
between staff officers in Tokyo in March 1942. In early April “Magic”
intercepts reached Australia which confirmed that no invasion was
contemplated. An actual danger of invasion had never existed and the
likelihood diminished through 1942 as Allied victories eroded Japan’s
offensive capability. Curtin was told as much by London and Washington,
and MacArthur, Curtin’s principal strategic adviser, consistently advised that
it was improbable. Why did Curtin continue to bang the invasion drum?
http://www.awm.gov.au/events/conference/2002/stanley_paper.pdf p.8
How was Curtin to know whether or not the Magic intercept was accurate, or even enemy disinformation?
All the evidence from 7 December 1941 to April 1942, including Japan’s repeated demands for Australia’s surrender and its steady advance towards Australia, was that it intended to invade.
All the evidence in the second half of 1942, from the Battle of the Coral Sea to the advance over Kokoda and the rest of the Papuan campaign to the Guadalcanal campaign, was that Japan was aiming to invade Australia.
We know now that that was not the case.
Nonethless, the Principal Historian at the AWM maintains that Curtin should have relied upon an isolated Magic intercept and assurances from others that Japan wasn’t going to invade when everything he could see at the time screamed exactly the opposite.
Coming back to Japan’s surrender, we know now that Japan was putting out peace feelers for a few months before it caved in, and that America was intercepting Japanese coded traffic that confirmed it was inclined to look for a negotiated peace. So? In October-December 1941 Japan was, apparently, negotiating with America to avoid a war despite having decided in July 1941 to go to war if it couldn’t get what it wanted by negotiation. It then launched a surprise attack on Pearl Harbor, Malaya, the Philippines etc. Why would anyone with that recent knowledge put any trust in Japan’s purported attempts to negotiate peace while it refused to adopt the simple course of accepting unconditional surrender?
Why would anyone who had experience of Japan’s ferocious defence on the islands nearing Japan infer anything other than that it would get worse rather than better the nearer they got to the Japanese heartland?
People can only act on what they know at the time, even if it might cause a tragedy which could have been avoided if they had been fully aware of all relevant factors.
There was no reason on what was known at the time not to drop the atomic bombs. On what was known at the time, there was every reason to drop them.