“It was the short men that caused all the trouble in the world.”

Source: A Long Way Down

Country Town Sayings (1911), p193.

Often paraphrased as "The whole problem with the world is that fools and fanatics are always so certain of themselves, but wiser people so full of doubts."
Compare: "One of the painful things about our time is that those who feel certainty are stupid, and those with any imagination and understanding are filled with doubt and indecision." B. Russell, New Hopes for a Changing World (1951). Compare also: "The best lack all conviction, while the worst / Are full of passionate intensity." W. B. Yeats, The Second Coming (1919).
See also: Dunning-Kruger effect, Historical Antecedents https://en.wikipedia.org/wiki/Dunning–Kruger_effect#Historical_antecedents.
1930s, Mortals and Others (1931-35)

As quoted in NEA Journal : The Journal of the National Education Association‎ Vol. 41 (1952) p. 300
Context: One of the basic causes for all the trouble in the world today is that people talk too much and think too little. They act too impulsively without thinking. I am not advocating in the slightest that we become mutes with our voices stilled because of fear of criticism of what we might say. That is moral cowardice. And moral cowardice that keeps us from speaking our minds is as dangerous to this country as irresponsible talk. The right way is not always the popular and easy way. Standing for right when it is unpopular is a true test of moral character. The importance of individual thinking to the preservation of our democracy and our freedom cannot be overemphasized. The broader sense of the concept of your role in the defense of democracy is that of the citizen doing his most for the preservation of democracy and peace by independent thinking, making that thinking articulate by translating it into action at the ballot boxes, in the forums, and in everyday life, and being constructive and positive in that thinking and articulation. The most precious thing that democracy gives to us is freedom. You and I cannot escape the fact that the ultimate responsibility for freedom is personal. Our freedoms today are not so much in danger because people are consciously trying to take them away from us as they are in danger because we forget to use them. Freedom unexercised may be freedom forfeited. The preservation of freedom is in the hands of the people themselves — not of the government.

“Because you are awake.”
Source: The Tales of Alvin Maker, Heartfire (1998), Chapter 4.

Attributed to Butler in: American Dental Association (1959) The Journal of the American Dental Association. Vol 59. p. 289

Actually a remark by Nicholas Murray Butler.
Quoted by Watson in comments about "Think" and attributed to Nicholas Murray Butler - IBM Archives: Comments on "THINK" - Transcript https://www-03.ibm.com/ibm/history/multimedia/think_trans.html
Misattributed
Source: American Dental Association (1959) The Journal of the American Dental Association. Vol 59. p. 289.

Source: Trouble