"Four shillings."

"Ah, quite so; you might have told me at once."

Experience has shown that no time in life precludes the acquirement of
new knowledge and new habits by one who thinks it worth while to make the
attempt. The elderly person will be surprised at his progress if he will
bring to bear upon a new subject a mind free from doubts of its usefulness,
doubts of his own ability, worry lest he is wasting valuable time, regrets
for the past and plans for the future.

It is not always possible to say just where useful habit merges into
obsession. A certain individual, we will say, invariably puts on the
left shoe before the right. This is a useful habit, fixed by constant
repetition, useful because it relieves the brain of conscious effort. But
suppose he decides some morning to put on the right shoe before the left;
this new order so offends his sense of the fitness of things that he finds
it hard to proceed; if he perseveres, his feet feel wrong to him; the
discomfort grows until finally he is impelled to remove the shoes and
replace them in the usual order. In this case an act which started as a
useful habit has been replaced by an obsession.

Suppose, again, a person obsessed by the fear of poison is prevented from
washing his hands before eating. He sits down, perhaps, fully intending to
proceed as if nothing had happened, but the thought occurs to him that he
may have touched something poisonous, though his reason tells him this
is most improbable. He reviews the events of the day and can find no
suggestion of poison; still the thought of poison obtrudes itself, and he
finds it impossible to put anything which he touches into his mouth. He