Fallacy of Composition

Fallacy of Composition
 * Claiming that because a statement is true of the parts, it must be true of the whole.

"Everything is made of atoms. Atoms are invisible to the naked eye. Therefore everything is invisible to the naked eye."

Fan Works

 * This trope can be a result of Author Appeal. For example: "Harry Potter is awesome. Goths are awesome. Therefore a fanfic which combines them should be awesome."

Film

 * Wild Wild West. Will Smith and Barry Sonnenfield were a great team with Men in Black, so any movie made by this pair will be a hit.
 * This happens in movies as well. Some films with an All-Star Cast, such as Yellowbeard and Town and Country, have been colossal flops.

Music

 * Occasionally, musicians from a number of different bands may come together and form a "Supergroup" with the overall hype being that the sum of the supergroup's parts are better than the original bands they came from (i.e. Velvet Revolver, Audioslave), only for it all to end up being unlistenable rubbish.

Tabletop Games

 * The Thirty-One Official Flavors in Paranoia currently include Vanilla-Prune, and Strawberry-Lobster is due to be rotated in next year.

Theatre

 * Cirque Du Soleil and Criss Angel are both popular, so it was believed that a collaboration between the company and the magician on a Las Vegas magic show was money in the bank; instead, Criss Angel -- Believe became a huge flop.

Western Animation

 * The Simpsons - Sideshow Bob's plan to kill Bart at Five Corners

Real Life

 * The classic trick question "which is heavier, a ton of feathers or a ton of lead?" works because of this fallacy; the hope is that the person answering will think that because individual feathers are light, a measured weight of them would be lighter than the same weight of something normally thought of as "heavy."
 * Some trick questions go even further and make the feathers the right answer, by using different measures of weight.
 * There's a mess of "tun" or "tonnage" measures... of volume, ie: tun, tonnage, shipping ton. Most pertain to ocean-going cargo ships. Feathers do pointlessly add a huge amount of volume, for any given constant weight. For that matter, the railway gross ton mile is the product of total weight (including the weight of lading cars and locomotives) and the distance moved by a train. A ton of feathers, plus the container to hold them all, gets bulky quickly.
 * Internet filters rely on this trope. Imagine why Pakistan blocked all of Facebook because of just one group.
 * The same is true of word filters: written erotica may mention breasts, but blocking all uses of the word blocks out gynaecology, chicken recipes, breast cancer prevention/treatment and other innocent uses. The "Scunthorpe Problem" nets even more collateral blocking (while the devious perverts just use word-substitution tricks).
 * There are also risks of extensive collateral damage if a system like communist China's Great Firewall blocks services by IP address. "Uncyclopedia is bad, Uncyclopedia Taiwan hides behind Cloudflare, therefore Cloudflare and everything hosted through Cloudflare is bad..." is sadly par for the course in some nations.
 * Any artistic endeavours which employ several superstars within their respective fields and hope the lightning strikes again can fall prey to this trope. For one example, the game Shadows of the Damned features the work of three famous Japanese developers. The result, while positively received, was not considered a gift from the gaming gods. Likewise, David Hayter, Dave Gibbons (not Alan Moore, though), and Zack Snyder put out the Watchmen movie and received similarly lukewarm reviews.
 * Alternative health claims are rife with these. The claimants will say that X is in a drug/food/compound, and therefore that the substance is healthful/unhealthful. For example, one fad claims that Splenda is toxic because it contains the element chlorine. It does. So does table salt. That's a classic example of this fallacy. A less unreasonable claim is that chloro-carbons (like Splenda) are unhealthful, while ionic chlorine (such as salt) is fine. This claim does not run afoul of this fallacy, though "Splenda is toxic at any reasonable dose" is not accepted by mainstream evidence-based medical practitioners. Food additives go through extensive toxicity testing before approval.
 * Dihydrogen monoxide, on the other hand? Deadly stuff. Sadly, it will take a disaster of titanic proportions with thousands killed before anyone acknowledges the true danger.