Australia wrapped up a 4-1 series victory with a two-wicket success via the Duckworth-Lewis method in Sydney on Sunday, chasing a revised target of 275 after the tourists had posted 6-280.
The win confirmed Australia's status as the number one side in the world in the 50-over format, ahead of the World Cup hosted by themselves and New Zealand in February and March next year.
For South Africa, who are now without an ODI fixture until January, the series loss to Australia perhaps leaves more questions than answers.
"Obviously, we're hurting. It's not ideal and it's not what we planned to do," said De Villiers, who did not play in Sydney.
"Maybe we over-thought things; maybe we've been over-analysing things a little bit.
"Sometimes when you talk about something a bit too much, you put so much emphasis on it that pressure on yourself that you do funny things in those situations.
"We put a lot of emphasis on powerplays. I put a lot of emphasis on our fielding and those were the areas that let us down quite a bit.
"Maybe I must stop talking about the little things we mustn't do and start talking about the things we should do.
"Had we done the basics a bit better, we probably could have won more than just one game.
"It's very disappointing knowing that we didn't do the basics well. It's the kind of thing a consistent cricket team needs to do to be successful all the time.
"It was just a poor performance all round - inconsistent. There is nothing more to say really. We know the areas that we need to work on.
"We know more or less which players to rely on in pressure situations and we've got a better idea of our World Cup squad moving forward."