Be careful how you use worthwhile
Speaking of a great vedantin and religious leader, a writer says: ‘The unassailable logic of his metaphysical works has stood the test of time and very few scholars of real merit of later days have thought it worthwhile to refute it’ –Saptagiri, April 2007, p.36.
What the writer wants to say is how rigorous and unassailable his author’s logic is.  This he does say in the first part of his sentence.  But then the second part seems directly to contradict it.  ‘…very few scholars of real merit …have thought it worthwhile to refute it.’ This gives an impression that the vedantin’s work is not worth the effort to refute it.
It doesn’t deserve all that attention.
How does this happen?
For one thing, notice that the two parts of the sentence are logically unconnected.   There is, of course, the conjunction and. But this simply brings the two clauses together suggesting no necessary connection between them. Supposing the writer had said: The unassailable logic of his metaphysical works is such that very few scholars of later days have thought it worthwhile to refute it.  Now the lack of initiative on the part of later scholars is clearly explained. The two clauses are connected in terms of ground and consequence.
Even so this is not the best the writer could have done.  He should have eschewed the use of worthwhile.  In affirmative sentences it has a positive suggestion: ‘worth doing’.
It is worthwhile spending time on meditation.  Solving So do ku   is a worthwhile occupation for students. 
But in negative sentences worthwhile has the effect of degrading the subject. The book was launched with a great deal of publicity.  But few reviewers thought it worthwhile to review the book.  (=Reviewers did not think it worthwhile to review the book.  Notice how a negative word like ‘few’ translates into a negation in the predicate when the sentence is interpreted. )  It is this phenomenon that gives us the impression that later scholars of ‘real merit’ thought that the vedantin’s work was not worth reviewing.
It can now be seen that a sentence like: The unassailable logic of his metaphysical works was such that few scholars of later days dared to attempt refuting it is absolutely unproblematic.

Sri Ramachandran wants to know whether we can have: Each to one’s own as a solution to the problem of non-sexist reference. 
The suggestion has been made by quite a few in the literature. But it has its own limitations.
The indefinite pronoun one has many uses but two are relevant here. As a pronoun referring to persons, one can refer to people in general, including the speaker or it can refer to the speaker alone.
One should always do one’s duty.  The reference here is to people in general, with the speaker included.  Indeed this use is the most frequent use of one (as Zandvoort points out). Here is another example. (from the same source). One must allow oneself a rest from time to time.
The other use of one is seen in a sentence like One was reluctant to turn down the invitation in spite of some recent misunderstanding. This use of one has been condemned from Fowler onwards.  For a particularly pompous and ridiculous use of one in this sense, see the entry ‘impersonal one’ in my Structure, Style, and Usage (OUP, 2005).
Consider now the sentence Each should take responsibility for what one does.  This has the meaning each person should take responsibility for what one does.  It can also mean: ‘Each person should take responsibility for what I do!’ This may look outrageous but the suggestion can’t be ruled out.
Thus although in some cases (Each to one’s own) one may seem a good substitute for a gender-marked pronoun like his / her, in general it is not a good non-sexist substitute. I will stick to Each to his own.

Rule of thumb
On most daily occasions we do things by rule of thumb rather than exact measurement and precise theory. You should let the water boil for a minute or two before dipping in the tea bags. Here we have a rule of thumb. But how did the phrase originate and what is its connection with thumb?
An account which I find particularly interesting is this. In earlier days in England, a man was allowed to beat his wife with a stick not bigger in thickness than his thumb. So this was the first Rule of Thumb.
Another account has it that brew masters often tested the temperature at which a batch of beer was brewing by dipping a thumb in the brew.
Both accounts seem plausible but the first one is definitely more interesting.