Many people insist that this is all fortuitous can mean. But people for decades have used the word in reference to happy accidents, as in The company's third-quarter profits were enhanced as the result of a fortuitous drop in the cost of RAM chips. This use may have arisen because fortuitous resembles both fortunate and felicitous. Whatever its origin, the use is well established in the writing of reputable authors. This use dates back at least to the 1920s, but people still widely regard it as incorrect, and you may want to avoid it.
People often confuse the verbs founder and flounder.
This usage is all right, but it may invite misunderstandings in contexts in which someone could infer a deprecatory interpretation. You may unintentionally offend someone by saying I offer you my most fulsome apologies, where the use of an adjective like full or abundant would leave no doubt about the sincerity of your intentions. All rights reserved.