What does everyone think is the biggest mistake that most of the contenders made?

I think it can be summed up by having such an overwhelming belief in their own abilities that they feel it to be a sign of weakness to ask questions: vis the saga of the coffee milk and not asking the shopping channel people for advice on what and how to sell.

I think the biggest mistake that most individuals make is that, because they have to complete the task in a limited timeframe, the pressure forces them to make many decision at too early a stage. Planning things through and considering the consequences is really important and will often save time later – but this is extremely difficult when you are in a competition.

It's hard to tell what they did and didn't ask. Simon picked the wheelchair because he was told it sold well, for example, but we weren't shown that.

Thinking that being made project manager means having sole control of the task with the other contestants being there just to do your bidding. Project management is about harnessing resources effectively (people and materials), collating information, scheduling, etc - very often the project manager is the least creative member of a team, they're harnessing and directing the energy not producing it.

The worst offender must have been Rory who evidently thought that the way to behave was to flashback to his public school days and behave like a head prefect with the new boys.

The biggest mistake anyone could make on the apprentice is telling Sir Alan that you are like him, started from nowhere and all that rubbish...

The biggest mistake is doing kissograms and the like despite 3 series worth of people being told off for it.

I agree

No research.

The last mistake is that they don't find out about their target - Amstrad and SAS. Better still if they could find out what the job is.

The first one is that they embellish their CV's - though they may need to to get selected for the show with so many applicants. They are then stuck with it.

In between they fail to watch enough people doing well to find out how. If you want to watch how to lead a team the second US series shows you what looks really good if you watch the winner. The third US series is a masterclass from Kendra in how to win tasks (do some market research , get the target market right and target it) and how to time your run (let idiots fail early, make important contributions and then start leading yourself when most of the difficult idiots have gone) You probably have to watch the US series because the UK examples are nothing like as good.

As SAS is somewhat random in his decisions, though, it may do you precisely no good at all......