Return to the fictional examination case. Registration makes a student generally eligible, presentation of an entry card is a condition, and an active suspension prevents admission. Even if registration and identification are established, admission does not follow while the suspension remains.
A cause or occasion connects a ruling to a circumstance; a condition is required for an effect; an impediment can block the effect even when other factors are present. These are technical relationships and should not be identified casually with every everyday “reason.”