Every physician can add much to his stock of knowledge by a proper review of cases which have come under his care. But a faulty mode of doing this will lead him into error. For example, one physician is so exceedingly fearful that in those cases, in which death has occurred, something which he did or left undone was the cause of the fatal event that he sees nothing clearly, and arrives at no definite and available conclusions; and he ends every review with nothing but unavailing regrets. Another, on the contrary, is too self-confident, scarcely harboring the idea that he could have ever committed any error. This notion of infallibility, though not distinctly avowed, is indulged to a greater or less extent by many physicians. If they do not think that they _never_ err, they at least think that it is very uncommon for them to do so. To such the past is worth nothing as corrective. They add from it nothing to their stock of ascertained facts, though they may add to their medley of true and false inferences. Both of these extremes should be avoided. The physician, in reviewing his cases, should not fear to find errors; for if he investigated them properly at the time with the best lights which he could command, and acted in good faith, he is not to be blamed if he did err. But, on the other hand, he should not pronounce any measure which he has adopted to be an error without substantial evidence. The disposition to form conclusions from a limited number of facts is a fertile source of error in medical observation. This has already been alluded to in previous chapters. This disposition is very common among young physicians. A small number of cases is often sufficient to lead them to adopt conclusions, which a larger number of cases would show to be false. The fact that their experience has been limited should teach them to be cautious in their inferences; but very often this caution is never learned, till a larger experience has revealed to them their errors. The disposition under consideration is often increased, and sometimes rendered inveterate, by the practice, so common especially among young aspirants for medical fame, of speaking quite freely in non-professional circles of the results of their experience. This practice is not only disgusting, but it contributes essentially to the establishment of a habit of loose observation and reasoning. But the disposition to adopt conclusions from a limited observation is by no means confined to young practitioners. It is a very common error in the profession at large; and the annals of medical experience are loaded down with errors, which come from this source. A few illustrations will suffice.