e or two facts that help him. He is most
likely to have noticed _where_ he was in the puzzle when his
accidental success occurred; for it appears that _locations_ are about
the easiest facts to learn for men as well as animals. In the course
of a few trials, also, the human subject notices that some lines of
attack are useless, and therefore eliminates them. After a time he may
"see into" the puzzle more or less clearly, though sometimes he gets a
practical mastery of the handling of the puzzle, while still obliged
to confess that he does not understand it at all.

{316}

Insight, when it does occur, is of great value. Insight into the
general principle of the puzzle leads to a better general plan of
attack, and insight into the detailed difficulties of manipulation
leads to smoother and defter handling. The human "learning curve" (see
Figure 50) often shows a prolonged stretch of no improvement, followed
by an abrupt change to quicker work; and the subject's introspections
show that 76 per cent, or more of these sudden improvements followed
immediately after some fresh insight into the puzzle.

[Illustration: Fig. 50.--(From Ruger.) Curve for human learning of a
mechanical puzzle. Distance above the base line represents the time
occupied in each trial, the successive trials being arranged in order
from left to right. A drop in the curve denotes a decrease in time,
and thus an improvement. At _X_, the subject saw something about the
puzzle that he had not noticed before and studied it out with some
care, so increasing his time for this one trial, but bringing the time
down thereafter to a new and steady level.]

The value of insight appears in another way when the subject, after
mastering one puzzle, is handed another involving the same principle
in a changed form. If he has seen the principle of the first puzzle,
he is likely to carry over this knowledge to the second, and master
this readily; {317} but if he has simply acquired motor skill with the
first puzzle, without any insight into its principle, he may have as
hard a time with the second as if he had never seen the first.

Learning by Observation

"We learn by doing" is a true proverb, in the sense that we acquire a
reaction by making just that reaction. We must make a reaction in
order to get it really in hand, so that the proverb might be
strengthened to read, "To learn, we must do". But we should make it
false if we strengthened it still further