Forbidden state or minimum floor

Name the one line that must never be crossed, or the number that must never drop below a set level. State it as a hard threshold with a value, not a direction like "stay safe" or "keep enough cash on hand."

Name the one line that must never be crossed, or the number that must never drop below a set level. State it as a hard threshold with a value, not a direction like "stay safe" or "keep enough cash on hand."

Example

For the hike: no one is above the treeline after 3pm, and nobody continues once the slowest member cannot hold a conversation while walking. Two hard lines with numbers, not "we'll turn back if it gets late."