Well aside from the simple answer; "Cos the Tories will be worse!", I think we should be bold in equally assessing publicly our failures and successes. If we hide our failures then we insult the electorate who can see them, if we hide our successes we not only let ourselves down, but also those vulnerable members of society who have much benefited from the last thirteen years.
So here it is, an assessment of where Labour is:
1/ Lessons the Labour Party has learned from its mistakes in the last years of government
First of all we have screwed up on Iraq. Big time! Esp on matters of trust. We also were too timid in putting forward strong Social Democratic ideas, too slow in looking at electoral reform (although there is some hope), too critical of opposition to New Labour, too bullying, too afraid to be radical and frail in what we need to do. We also should have kept distance with the Bush administration and for that we are truly sorry. However...
2/ Why another five years of Labour rule is still preferable to a Tory rule
For a start there are more civil rights for gay couples, we have helped bring stability to Northern Ireland, have brought in the New Deal, the National Minimum Wage (which the Conservatives and Liberal Democrats opposed), the banning of Fox Hunting, substantially increased child benefit, introduced the disability rights commission, free TV licences for over-75s and more.
If Labour win, added to that will be electoral reform, a continual move away from the recession (we are now at 0.5%), and no cuts to Education and Health, which the Tories will bring in because, given past records, when they have made cuts, they have always slashed away at areas where people are in desperately vulnerable situations.
I know I have touched on this before, but let us be honest, let us be penitent, but let us also be confident and put forward our case as to why a Labour Government is better than a Conservative one.