Well, for starters, I very much doubt you, or any average joe, is prepared Cardio wise. It's nothing against you personally, it's the fact that Boxing is more demanding in terms of Cardio than almost any events out there. I could make a very decent argument about how it's more intensive than swimming, marathons and other cardio related sports because of multiple reasons, but I will talk about the major issue.
The fact is, that boxing matches end under only two circumstances, apart from some outliers: either a knockout, or both fighters lasting until the end. Assuming, we are talking in terms of professional, high level bouts, that's 12 rounds of 3 gruelling minutes with an opponent who's sole aim for the next half an hour is beating the snot out of you. Even in amateur, beginner level exhibition fights, back at home I believe it was 5 rounds of 1 minute, the fighters are completely gassed by the end. The fact is, that boxing and other similar sports, are the only type of physical challenges that require you to give your all until you or your opponent drops, or for a full 36 minutes. In comparison to, say, swimming, in which the longest event (in personal experience) is a 1600m swim, you can pace yourself to stretch out your stamina for the whole event. And even when pacing yourself, it is uncommon at amateur level to swim for more than 25 minutes. The level of output required in boxing is insane, and you only get to pace yourself in a match if your opponent lets you. There is no one, anywhere in this world, who can go all out (as you would in a boxing match) and not feel like a pig in a sauna for days on end afterwards.
As for raw punching power, that only gets you so far. The best recent example I can think of, are Tyson Fury's matches vs Deontay Wilder. Granted, Deontay Wilder's punching power allowed him to get to world champion. But he was very severely outclassed
twice by The Gypsy King due to Tyson's technical know-how and Deontay's lack of technique. I mean the two punches he landed on Fury in the first fight were devastating enough to knock him down, but he was dominated severely throughout the entire fight.
Lastly, I want you to think about a very important question. Assuming, and average Joe would want to compete, what would his motivation be? This is perhaps the most defining characteristic of whether you will succeed or you won't. You stated in another thread that boxing, or martial arts aren't your passion. That's fair enough. But are you boxing in an attempt to impress others? To build yourself up? Many people overlook this but belief and
reason has been the driving factor in many world events - from breaking the expectations that the 4-minute mile couldn't be done, to something much more relevant to the topic.
Mike Tyson's defeat to Buster Douglas
Going into the fighter, James "Buster" Douglas was a 42-1 underdog, and people payed not to watch a fight, but what was supposed to be a stone-cold beat down - straight up murder. Unbeknownst to many, Buster spoke about why he won, and why he wasn't afraid going into the match as many fighters had been, in his situation. Buster won, because his mother who had passed away merely weeks before the fight.
"My son James, is going to beat Mike Tyson!"
I hope that answers your question. Your chances of whether you will last or you will fizzle in the world of boxing and martial arts is your why.