Everyone can recognize history when it happens. Everyone can recognize history after is has happened; but only the wise man knows at the moment what is vital and permanent, what is lasting and memorable.
The scientific theorist is not to be envied. For Nature, or more precisely experiment, is an exorable and not very friendly judge of his work. It never says "yes" to a theory. In the most favorable cases it says "Maybe," and in the great majority of cases simply "No." If an experiment agrees with a theory it means for the latter "Maybe," and if it does not agree it means "No." Probably every theory will some day experience its "No" - most theories, soon after conception.
If there be no great love in the beginning, yet heaven may decrease it upon better acquaintance, when we are married and have more occasion to know one another: I hope, upon familiarity will grow more contempt.