"When he has to write many letters, sometimes a sudden fear gets possession of him that he has interchanged the letters and put them into the wrong envelopes. He has then to tear open the envelopes and look the letters over again and again, to assure himself that they have been put by him into the right envelopes. "Similarly, in turning out the gas jet, he must needs try it over again and again, and is often forced to get up from bed to try again whether the gas is 'really' shut off. He lights the gas, then tests the gas jet with a lighted match, to see whether the gas leaks and is 'really' completely shut off. "In closing the door of his room, he must try the lock over and over again. He locks the door, and then unlocks it again, then locks it once more. Still, he is not sure. He then must shake it violently, so as to get the full assurance that the door has been actually and 'really' locked."[11] This second illustrative instance brings out vividly a fact that deserves to be emphasised--the fact, namely, that, at bottom, these doubting manias are only exaggerations of a phenomenon of common occurrence. There are times when virtually everybody is tormented by doubts regarding matters that ought not to cause any indecision or perplexity. Moreover, while comparatively few people feel the need of going to a physician to be cured of abnormal doubting, there are many others who might advantageously seek the specialist's aid. People are often blind to their great weakness in this respect, though their friends may see clearly that their vacillation with regard to things great or small constitutes a defect that of itself accounts amply for their inability to make headway in the world and rise above mediocrity. Like the Washington neurologist's patient, if in less degree, there are people to whom the choice of clothing presents a prodigious problem. To others, the choice of foods is a never-ending puzzle. At every meal they find themselves sadly at a loss to decide what they shall eat. Others, again, acting in much the fashion of the young man treated by Doctor Sidis, conjure up visions of possible mistakes and mishaps in connection with the writing and mailing of letters, the opening or shutting of doors and windows, the carrying of umbrellas, etc. Also, there are doubters of a kind well described by an observant physician: "There are people who doubt whether their friends really think anything of them. They think that, though they treat them courteously, this may be only common politeness, and that they may really resent their wasting their time when they call on them. They hesitate to ask these people to do things for them, though, over and over again, the friends may have shown their willingness, and, above all, by asking favours of them in turn, may have shown that they were quite willing to put themselves under obligations.