I've been thinking, and writing, about The Impossible Question of the Thyroid for some while now.
I came up with what I thought was a good stab at an answer to its majestic mystery:
http://lesswrong.com/r/discussion/lw/nef/the_thyroid_madness_core_argument_evidence/
This is a very simple and obvious explanation of an awful lot of otherwise confusing data, anecdotes, quackery, expert opinion and medical research.
People seem to hate it because it is so simple, and makes so many predictions, most of which are terrifying.
And it is obviously false! Of course medicine has tried using thyroid supplementation to fix 'tired all the time'. It doesn't work!
EDIT: Apparently I spoke too soon. GRB Skinner tried it in 2000, and it works a treat. See comments.
But there really is an awful lot unexplained about all this T4/T3 business, and why different people think it works differently. I refer you to the internet for all the unexplained things.
In just the endocrinological literature there is a long fight going on about T4/T3 ratios in thyroid supplementation, and about the question of whether or not to treat 'subclinical hypothyroidism'. Some people show symptoms with very low TSH values. Some people have extremely high TSH values and show no symptoms at all.
I've been trying various ways of explaining it all for nearly four months now. And I've found lots of magical thinking in conventional medicine, and lots of waving away of the reports of honest-sounding empiricists, real doctors, who have made no obvious errors of reasoning, most of whom are taking terrible risks with their own careers in order to, as they see it, help their patients.
I've read lots of people saying 'we tried this, and it works', and no people saying 'we tried this, and it makes no difference'. The explanation favoured by conventional medicine strongly predicts 'we tried this, and it makes no difference'. But they've never tried it!
It's really confusing. A lot of people are very confused.
I think that simple explanations are extra-worth looking at because they are simple.
Of course that doesn't mean they're right. Consequences and experiment are the only judge of that.
I do not think I am right! There is no way I can have got the whole picture. I can't explain, for instance: 'euthyroid sick syndrome'. But I don't predict that it doesn't exist either.
But you should look very carefully at the simple beautiful ideas that seem to explain everything, but that look untrue.
Firstly because Solomonoff induction looks like a good way to think about the world. Or call it Occam's Razor if you prefer. It is straightforward Bayesianism, as David Mackay points out in Information Theory, Inference, and Learning Algorithms.
Secondly because all the good ideas have turned out to be simple, and could have been spotted, (and often were) by the Ancient Greeks, and could have been demonstrated by them, if only they'd really thought about it.
Thirdly because experiments not done with the hypothesis in mind have likely neglected important aspects of the problem. (In this case T3 homeostasis, and possible peripheral resistance, and the difference between basal metabolic rate and waking rate, and the difference between core and peripheral temperature, and the possibility of a common DIO2 mutation causing people's systems to react differently to T4 monotherapy, and in general the hideous complexity of the thyroid system and its function in vertebrates in general).
Fourthly because the reason for the 'unreasonable effectiveness of mathematics' is that the simplest ideas tend to come up everywhere!
And so when a mathematician plays with a toy problem for fun, and reasons carefully about it, two thousand years later it can end up winning a major war in a way no one ever expected.
So that even if there are things you can't explain (I can't explain hot daytime fibro-turks...), you should keep plugging away, to see if you can explain them, if you think hard enough.
Good ideas should be given extra-benefit of the doubt. Not ignored because they prove (slightly) too much!
Do not believe them. Do not ever ever believe them. You will end up worse than Hitler. You will end up worse than Marx.
But give them the benefit of the doubt. Keep them in mind. Try safe experiments, ready to abort when they go wrong.
And if they're easy to refute (mine is), then if you're going to call yourself a scientist, damned well take the trouble to refute the things. You might learn something!