Try to use the Edit-button...
Another thing to consider is that no-one is perfect - people make mistakes, and leaders are especially prone to pushing even really bad decisions through, if only to keep their positions. Just look at our politicians of today.
Then there are political wingfights, which sometimes lead to bad decisions just because of the entrenchment of the two (or more) sides. The US for instance lost a lot of opportunities for peaceful or easily achievable expansions just because local politicians were afraid of cheap labor, of administrative difficulties, of being considered "imperialist", and the likes.
Another factor is popular sentiment - sometimes, politicians have to make really bad decisions to keep their subordinates from revolting, sometimes they can't do really good decisions unless they want a revolt.
Also, many decision makers let their personal interests stand above national interests - GB could have had breach loaded rifles in the ARW already, had there not been a lot of personal relations between military brass and the traditional suppliers (and some in hindsight silly arguments about high firing rates for soldiers forced into service).
Than there is the problem of decision makers being too involved in the details to see the broad picture. I remember for myself deciding to order PCs without hard disk for an organisation just when they were getting popular - a year later, they had to be purchased separately (at a high price), as most new programs didn't run without them anymore (yes, I'm *really* old
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And so on.
I suppose many leaders knew their decisions were bad, or at least risky, when they took them, but didn't see a choice or didn't want to take the best decision for other reasons. Some just realized soon after word was out, and couldn't go back - people who don't like counselling with every side on every matter are prone to that, especially as sometimes a few bad apples among mostly good apples are better than no apples at all - at least in their (and popular) perception.
Which is why hindsight is so difficult to keep away. With hindsight, one could turn any stone age civilisation into a modern information society spanning the whole globe within a few decades, or at least centuries.