Flounder vs Founder

In the series 'words almost spelled the same and almost mean the same thing, but are not'

Both mean many things but they come closest as things that happen to you metaphorically relating to the sea.

Flounder is the flat fish, and to flounder is to be like a flounder on the deck of a ship and flail about.

Founder, on the other hand is one who starts something (very different!) because they are at the base of things (cognate with the foundation). 

But to founder is not to found something but to begin the process of sinking, to founder upon the shoals. 

Certainly a flounder could founder on the shoals if it put itself into such a bad position, but that is less likely than that a founder of an enterprise would flounder before pivoting to a greenfield market (count the mixed metaphors!).

The etymology of founder is incontrovertibly via French fond from Latin fundus, the bottom. Flounder, the fish, supposedly is cognate with flat (obvious) and plaice (obvious biologically but not immediately obvious phonetically). Despite my metaphor about a fish flailing about, to flounder however has a controvertible provenance, probably mixed up with other similar sounding words, like flop and flail and fluke (is that another fish) in an example of phonosemantics.

So flounder, fish, flop. Founder, sink to the profound bottom.