unplanned happenstance

spontaneous unexpected serendipity coincidence random chance accident sudden surprise casual unintentional haphazard unpredictable involuntary arbitrary unforeseen unpredicted undesigned incidental unpremeditated uncontrolled accidental unpurposeful fortuitous unsystematic unthinking unwitting unplotted inadvertent unconscious unreasoned unstudied unprogramming unintended unforced unchosen unarranged uncontrived unscheduled unkempt unfocused unwilled unstrained uncalculated unlooked unknown unsteady unrehearsed unplanned happenstance