NASA didn't plan to blow up a shuttle with people on board. But a combination of O-ring problems, cold weather and the pressure to launch created a perfect storm of bad decisions.
British Petroleum didn't set out to dump millions of gallons of oil into the Gulf of Mexico. But cutting corners on safety, ignoring warning signs and prioritising speed over caution led to an environmental catastrophe.
City officials thought they were saving money by switching water sources in Flint, Michigan. They had no intention of poisoning an entire city with lead. But they didn't treat the water properly and bureaucratic incompetence turned a cost-cutting measure into a public health nightmare.
Good intentions coupled with bad execution and a series of small compromises can snowball into major disasters.
Sometimes the worst outcomes happen when people are just trying to do their jobs and save some money and time.
I haven't met a single developer who sits down scheming how to exclude users with disabilities. But when they skip alt text because they're rushing to meet a deadline, ignore keyboard navigation because it's fiddly or choose colours that look trendy but fail contrast tests, they're making those same small compromises.
Each compromise seems harmless on its own. But together, they create websites that are completely unusable for millions of people.
You don't need a plan to fail at accessibility. You just need to not have a plan to succeed.