Avoiding mistakes is certainly highly desirable.  However it is also 
widely acknowledged that perfectionism is inimicable to creativity. 
And in ordinary life, perfectionism carried beyond a certain point is 
indicative of a psychological disorder.  In the extreme case, a  
perfectionist becomes so paralyzed by all the possible mistakes he might 
make that he is unable to even leave the house.  

In science, we want to discover as much truth about the world as possible 
and we also want to have as much certainty as possible about these 
discoveries.  Usually there is some trade-off between these two desiderata 
--- the search for scope and the search for certainty.  

If 18th century mathematicians had demanded total rigor from Newton and 
Leibniz then there would probably be no calculus today, because neither 
of the two could explain calculus in a way that really made sense, since 
they lacked the concept of a limit.  And in fact, because of the lack of 
a rigorous foundation, they made a number of errors in their use of calculus. 
It was only a hundred years later that Weistrass was able to give a solid 
grounding for the ideas of Newton and Leibniz.  Nonetheless, what Newton 
and Leibniz did was undoubtedly science and mathematics gained a great 
deal more from the application of their important ideas than it lost 
through the mistakes they made.  


These are not the rules according to many who post to sci.med and
sci.psychology.  According to these posters  "If it's not supported by
carefully designed controlled studies then it's not science."

Taken to the extreme, I believe that the attitude that empirical studies 
are everything and ideas are nothing results in a complete stultification 
of science.  

For one thing, an insistence on an elaborate and expensive methodology 
results in a sort of scientific trade-unionism, where those outside 
the establishment and lacking institutional or corporate support have 
no chance to obtain a hearing.  (I don't in the least believe that this 
is the intention of the arbiters of scientific methodology.  Nonetheless, 
it is one of the results.)   And although institutional science has 
certainly produced many wonderful results, I think it is a foolish 
arrogance for scientists to believe that no one outside the establishment 
--- and using less than perfect empirical methodology --- will ever come 
with anything worthwhile.  

Furthermore, the big bucks approach to science promotes what I think is
one of the most significant errors in science:  choosing to investigate
questions because they can be readily handled by the currently
fashionable methodology (or because one can readily get institutional
or corporate sponsorship for them) instead of directing attention to
those questions which seem to have fundamental significance.

For instance, certain questions cannot be easily investigated with
statistical methods because the relevant factors are not quantitative.
(One could argue that this is the case for almost all questions in many
areas of psychology.  In my opinion, a perusal of many of the papers
resulting from the attempt by psychologists to force these questions
into a statistical framework gives the lie to Russell Turpin's
assertion that current scientific methods "avoid all known errors.")

I think that asking the wrong question is probably the most fundamental 
error in science.  (Ignoring potentially valuable ideas is one of the 
others.)  And I think that scientific journals are full of all 
too many studies done with impeccable empirical methods but which are 
worthless because the wrong question was asked in the first place.  

--
In the arguments between behaviorists and cognitivists, psychology seems 
less like a science than a collection of competing religious sects.   