Product-channel fit: the product bends to the channel
The deepest reason channel selection is a discovery and not a free pick comes down to control. You control your product. You do not control the channel. The channel has its own rules, its own algorithm, its own economics, and none of them will bend to accommodate what you have built. So the adaptation can only flow one way: products are built to fit channels, channels do not mould to products. Get that direction right and the whole problem reorganises itself.
Three archetypes of fit
Look at how the winners did it and the pattern is unmistakable. The virality winners, the WhatsApps, Dropboxes, Slacks and Evernotes, made the product itself the channel. Sharing loops were engineered in, so distribution happened as a by-product of usage, and a second paid channel was unnecessary for years. The user-generated-content and SEO winners, the TripAdvisors, Yelps, Glassdoors, Pinterests and Houzzes, built the product so that using it generated the indexable content that fed the channel. The paid-marketing winners, the Supercells, Squarespaces and Blue Aprons, chose paid as their one channel and went deep on creative and unit economics rather than dabbling in organic and outbound on the side.
In every case the product was shaped to the channel's constraints. A viral product has sharing built into its core loop. An SEO product produces something worth indexing as a natural output. An outbound product targets a definable account list. None of these is an afterthought bolted on after the product was finished.
Channel choice is engineering, not media-buying
This is the reframe that separates founders who find fit from those who keep grazing. Channel selection is not a marketing decision you make once the product is built and the launch looms. It is an engineering decision, woven into what you build. If your distribution plan is "we'll figure out marketing later", you have already decided to bolt a channel onto a product that was not shaped for it, and the channel will not bend to forgive you.
Kill the silo
The practical implication is to refuse the wall between what you build and how you distribute. The teams that win do not have a product team that ships and a growth team that distributes whatever lands on the doorstep. They have one decision running through both: which channel are we fitting to, and what does the product have to be for that channel to work? Answer that early, build the product to honour it, and channel selection stops being a guessing game played after the fact. It becomes a design constraint you carry from the first line of the spec.