Why did Singapore fall if coherent defenses existed?

Why was there no coherent plan for Singapore's defense?

There were coherent plans, but some prepared positions were left unmanned as the staff and command system failed.

A viewer asks why Singapore lacked a coherent defensive plan. The premise is rejected because coherent plans and constructed positions did exist. The failure lay in execution: key sites, including defenses around the reservoir, were not properly manned. That gap followed the collapse of the staff and command system, which distinguishes a bad outcome from an absence of prior planning.