By Nick Assinder
Political Correspondent, BBC News website
As he told MPs before crashing to a Commons defeat, Tony Blair believes it is better to do the right thing and lose than do the wrong thing and win.
Blair will aim to explain reforms to MPs
It is a principle that is going to be tested to destruction over the coming weeks and months as he attempts to secure his legacy with a series of controversial and radical reforms.
Following his surprisingly decisive defeat over his anti-terror laws, the prime minister faces a pretty fundamental decision.
Does he listen to his emboldened backbench rebels and trim back his plans, something he has time and again promised to do in the wake of setbacks, only then to face claims he has quickly returned to his old, presidential ways?
Or does he decide that the only way to secure the legacy he longs for is to defy his rebels and press ahead regardless?
That is precisely what he did on Wednesday afternoon with the now well-publicised results.
Welfare proposals to include cuts to incapacity benefit published within weeks
Health plans which will boost role of private provision published early next year
Controversial schools legislation back before MPs in February
Other difficult issues include ID cards and Nuclear power
If he follows the first course, he may well remain in power but it might only be at the cost of his more radical proposals - not the legacy he has in mind.
If he pursues the second course, the current evidence suggests he will indeed do what he believes is the right thing, but lose and probably have to stand down.
Yet at the moment that appears to be his intention, telling the Cabinet these are manifesto commitments which the voters expect him to complete.
The issues could not be bigger, they include health, education, welfare, and the future of both nuclear power and nuclear weapons.
At his party conference in September, he confessed he wished he had gone further with his reforms over the past eight years.
And many reviewing his record believe he has indeed left any genuine radicalism to his self-pronounced last term.
Now, with his rebels stronger than ever, his majority smaller than ever and his premiership time-limited, he is trying to complete the reforms he admits he failed to do earlier.
Blairs school plans sparked controversy
On education, his plans to see every secondary school independent have already sparked a major Cabinet revolt led by his deputy John Prescott who believes they would destroy the comprehensive ideal - one of Labour's most cherished policies.
On health, proposals to increase the role of the private sector in the NHS has seen claims he is moving towards privatising the service and creating a two tier service.
On welfare, his intention of cutting incapacity benefit to help "enable" people back into work has been attacked as an attack on the most vulnerable and is said to have even led to a row with his ex-minister David Blunkett.
And the prime minister's refusal to rule out replacement of the Trident nuclear deterrent or turn to nuclear power to meet future energy demands has also sparked significant opposition.
The most likely is that he will attempt to square this circle by trimming enough to avert defeat - as he did on foundation hospitals - while attempting to salvage enough to stand as a legacy.
It is a difficult tightrope to walk at the best of times. Under these new circumstances with MPs shaking the rope, it may well prove impossible.