Any project even a quarter as complex as a manned lunar mission going to run into problems and failures and unforeseen complications (just ask anyone who's ever done any home renovation). Things go over budget, deadlines are missed, stuff doesn't work out the way you'd envisioned. This isn't always somebody's fault or the result of poor planning (though they can be).

Yeah, we've been there already, but it's been many decades and we haven't exactly kept all the tech and procedures up to date in the intervening years. And that first go-round itself missed it's intended deadline by about 7-8 years.