Halliday & Matthiessen (1999: 235-6):
On all these grounds we have to acknowledge that the metaphorical relationship is not a symmetrical one: there is a definite directionality to it, such that one end of the continuum is metaphorical and the other is what we shall call congruent. Thus given the pair
we shall locate the two with respect to each other on a metaphor scale as above. The expression engine failure evolved after the expression the engine failed in the evolution of industrial discourse; to explain in times of engine failure to a child you gloss it as whenever an engine failed (as one of the authors had to do to his 7-year-old son); the text would be likely to progress from loads were reduced, engines failed to reduced loading, engine failure rather than the other way round.
And when we derive one from the other, we find ambiguity in one direction only: reduced loading might be agnate to loads were reduced, had been reduced or were lighter than usual; engine failure might be agnate to an engine failed, the engine failed or engines failed, and to ... failed or had failed in each case.