The Cliffhanger Has to Pay Rent in the Next Episode
A sudden ending creates anticipation. The following episode decides whether that anticipation was earned.
A door opens, someone gasps and the episode ends. You are curious. That curiosity is only the first half of the cliffhanger's job.
The interruption needs a consequence
Filmmakers deliberately control what an audience sees and when, a principle visible in Hitchcock's account of his methods. Here is an original television test: imagine the interrupted moment resolved in the first minute of the next episode. What changes afterward?

Editorial image from Blogdel's entertainment collection, used for illustration.
If the discovery alters a relationship, creates a difficult choice or exposes a new problem, the ending has carried the story forward. If it is dismissed immediately and nothing changes, the interruption can feel like a trick to collect another click.
Watch the episode after the gasp
Look for the consequences rather than only the answer. A reveal can be ordinary but still useful if it forces an interesting decision. A spectacular reveal can be hollow if the characters resume their previous lives untouched.
This is a critical preference, not a universal rule for every serial. Some shows enjoy playful misdirection. Still, a rewarding cliffhanger tends to leave the next episode with work to do. Anticipation is borrowed attention; the story should give the audience a worthwhile return.

Editorial image from Blogdel's entertainment collection, used for illustration.
Sources and further reading
References
- Alfred Hitchcock: my own methods | BFI · primary