Plans Laid Best Laid Carefully Made Plans.  Ends Poorly

The most carefully made plans.  Said when something ends poorly or differently than expected, despite preparations for success. It is an abbreviated version of the full proverb "the best-laid plans of mice and men oft go astray."

We are not the masters of the external world. We cannot predict the future. Our best laid plans are always subject to catastrophic failure.

Even the best-laid plans sometimes go wrong.