Any time you're dealing with something that has a huge number of variables, many of which are random, this dynamic presents itself. The opposite is true, too. You can make a bad decision for all the wrong reasons, and it happens to work out in your favor. That a single decision (in this case, hiring a head coach) worked or didn't work in a specific instance doesn't retroactively make that decision better or worse.

If you were playing poker and your hand has an 80% chance of winning after you see the river card, playing it out is the right decision, even if it doesn't always work.