How important is honest and realism?

At a recent training event, there was good discussion on the virtues of honesty and realism, in particular how these values/behaviours likely make for better relationships/outcomes. My early experiences in UK construction seemed to have a distinct lack of either of these, in fact very close to the complete opposite. Presumably parties thought this approach meant that the client paid less or the contractor was paid more, depending on what side of the 'fence' you were. What I now finally and thankfully see emerging is at least the belief that if we all really acted in an open and constructive manner, and things such as programmes and tendered prices were indeed realistic, we are in much better shape to do sensible business and indeed the client side is far more amenable to helping the contractor achieve his objectives.

How do NEC Contracts support these? Not least through clause 10.1 mutual trust and the main contracts requiring realistic and practicable programmes. Not the be all and end all, but imagine starting with a good, sensible price (say a target cost). Then the contractor producing a challenging but realistic programme. Then there are discussions such as....
- oops, I realise now we've forgot to price/programme this activity...
- if I (the client) can't get this free issue item to you by that date, exactly where are we?
- have you thought about re-sequencing this part of the works because....
- what happens if....
- and so on.

If we put our efforts 100% into the project itself, being mindful there are (generally) 2 main parties who have objectives they each need to achieve, we can surely come up with some fantastic problem solving if indeed we are honest and realistic.

What do you think?