I you are referring to the two Space Shuttle accidents, both of them could have been avoided with just a little bit more care - not launching in freezing temperatures for Challenger, and making sure insulation foam doesn't fall off the tank for Columbia.

The history of rocketry goes much further back than the space shuttle. The shuttle was supposed to be a step towards reusability but didn’t succeed or progress the way they thought it would. Starship is continuing that dream of full reusability and their approach is working. You can’t plan everything on paper when it comes to hardware especially when attempting things that have never been done before, you just don’t have the data in that case. You have to build prototypes and test them to destruction. All manufacturers do this.

In hindsight yes. The trick is knowing which of the thousands of things to do are necessary. And yes, that’s how you end up with preflight checklists