When your pair actually moves
Forex Foundations
Pairs move in their own sessions
A currency pair tends to move most during the sessions tied to its own currencies. EUR/USD is most active during London and the London-New York overlap. USD/JPY picks up during the Asian session and the New York session both.
Wrong session, thin volume
Trading a pair during a session where neither of its currencies is particularly active often means thin volume and choppy, directionless movement, regardless of how clean the setup looks on the chart.
A real filter, not polish
Matching the pair to its most active session isn't optional polish, it's a real filter. The same setup on the same pair can behave completely differently depending on which session it prints in.